Process for the heterotrophic production of microbial products with high concentrations of omega-3 highly unsaturated fatty acids

ABSTRACT

A process for the heterotrophic or predominantly heterotrophic production of whole-celled or extracted microbial products with a high concentration of omega-3 highly unsaturated fatty acids, producible in an aerobic culture under controlled conditions using biologically pure cultures of heterotrophic single-celled fungi microorganisms of the order Thraustochytriales. The harvested whole-cell microbial product can be added to processed foods as a nutritional supplement, or to fish and animal feeds to enhance the omega-3 highly unsaturated fatty acid content of products produced from these animals. The lipids containing these fatty acids can also be extracted and used in nutritional, pharmaceutical and industrial applications.

Cross-Reference to Related Applications

This application is a continuation-in-part of copending and commonlyassigned U.S. patent application Ser. No. 07/439,093, filed Nov. 17,1989, and entitled "Process for Heterotrophic Production of MicrobialProducts with High Concentrations of Omega-3 Highly Unsaturated FattyAcids" now abandoned which is incorporated herein in its entirety byreference and is a continuation-in-part of U.S. patent application Ser.No. 07/241,410, filed Sept. 7, 1988, and entitled "Process forHeterotrophic Production of Microbial Products with High Concentrationsof Omega-3 Highly Unsaturated Fatty Acids" which was previouslyexpressly abandoned.

FIELD OF THE INVENTION

The field of this invention relates to heterotrophic organisms and aprocess for culturing them for the production of lipids with highconcentrations of omega-3 highly unsaturated fatty acids (HUFA) suitablefor human and animal consumption as food additives or for use inpharmaceutical and industrial products.

BACKGROUND OF THE INVENTION

Omega-3 highly unsaturated fatty acids are of significant commercialinterest in that they have been recently recognized as important dietarycompounds for preventing arteriosclerosis and coronary heart disease,for alleviating inflammatory conditions and for retarding the growth oftumor cells. These beneficial effects are a result both of omega-3highly unsaturated fatty acids causing competitive inhibition ofcompounds produced from omega-6 fatty acids, and from beneficialcompounds produced directly from the omega-3 highly unsaturated fattyacids themselves (Simopoulos et al., 1986). Omega-6 fatty acids are thepredominant highly unsaturated fatty acids found in plants and animals.Currently the only commercially available dietary source of omega-3highly unsaturated fatty acids is from certain fish oils which cancontain up to 20-30% of these fatty acids. The beneficial effects ofthese fatty acids can be obtained by eating fish several times a week orby daily intake of concentrated fish oil. Consequently large quantitiesof fish oil are processed and encapsulated each year for sale as adietary supplement.

However, there are several significant problems with these fish oilsupplements. First, they can contain high levels of fat-soluble vitaminsthat are found naturally in fish oils. When ingested, these vitamins arestored and metabolized in fat in the human body rather than excreted inurine. High doses of these vitamins can be unsafe, leading to kidneyproblems or blindness and several U.S. medical associations havecautioned against using capsule supplements rather than real fish.Secondly, fish oils contain up to 80% of saturated and omega-6 fattyacids, both of which can have deleterious health effects. Additionally,fish oils have a strong fishy taste and odor, and as such cannot beadded to processed foods as a food additive, without negativelyaffecting the taste of the food product. Moreover, the isolation of pureomega-3 highly unsaturated fatty acids from this mixture is an involvedand expensive process resulting in very high prices ($200-$1000/ g) forpure forms of these fatty acids (Sigma Chemical Co., 1988; CalBiochemCo., 1987).

The natural source of omega-3 highly unsaturated fatty acids in fish oilis algae. These highly unsaturated fatty acids are important componentsof photosynthetic membranes. Omega-3 highly unsaturated fatty acidsaccumulate in the food chain and are eventually incorporated in fishoils. Bacteria and yeast are not able to synthesize omega-3 highlyunsaturated fatty acids and only a few fungi are known which can produceminor and trace amounts of omega-3 highly unsaturated fatty acids(Weete, 1980; Wassef, 1977; Erwin, 1973).

Algae have been grown in outdoor cultivation ponds for thephotoautotrophic production of a wide variety of products includingomega-3 highly unsaturated fatty acid containing biomass. For example,U.S. Pat. No. 4,341,038 describes a method for the photosyntheticproduction of oils from algae, and U.S. Pat. No. 4,615,839 describes aprocess for concentrating eicosapentaenoic acid (EPA) (one of theomega-3 highly unsaturated fatty acids) produced photosynthetically bystrains of the green algal Chlorella. Photoautotrophy is the processwhereby cells utilize the process of photosynthesis to construct organiccompounds from CO₂ and water, while using light as an energy source.Since sunlight is the driving force for this type of production system,algal cultivation ponds require large amounts of surface area (land) tobe economically viable. Due to their large size, these systems cannot beeconomically covered, because of high costs and technical problems, andbecause even transparent covers tend to block a significant amount ofthe sunlight. Therefore, these production systems are not axenic, andare difficult to maintain as monocultures. This is especially criticalif the cultures need to be manipulated or stressed (e.g. nitrogenlimited) to induce production of the desired product. Typically, it isduring these periods of stress, when the cells are only producingproduct and are not multiplying, that contaminants can readily invadethe cultures. Thus, in most cases, the biomass produced is not desirableas a food additive for human consumption without employing expensiveextraction procedures to recover the lipids. Additionally,photosynthetic production of algae in outdoor systems is very costly,since cultures must be maintained at low densities (1-2 g/l) to preventlight limitation of the culture. Consequently, large volumes of watermust be processed to recover small quantities of algae, and since thealgal cells are very tiny, expensive harvesting processes must also beemployed.

Mixotrophy is an alternative mode of production whereby certain strainsof algae carry on photosynthesis with light as a necessary energy sourcebut additionally use organic compounds supplied in the medium. Higherdensities can be achieved by mixotrophic production and the cultures canbe maintained in closed reactors for axenic production. U.S. Pat. Nos.3,444,647 and 3,316,674 describe processes for the mixotrophicproduction of algae. However, because of the need to supply light to theculture, production reactors of this type are very expensive to buildand operate, and culture densities are still very limited.

An additional problem with the cultivation of algae for omega-3 highlyunsaturated fatty acid production, is that even though omega-3 highlyunsaturated fatty acids comprise 20-40% of some strains, total fattyacids, the total fatty acid content of these algae is generally verylow, ranging from 5-10% of ash-free dry weight. In order to increase thefatty acid content of the cells, they must undergo a period of nitrogenlimitation which stimulates the production of lipids. However, of allthe strains noted to date in the literature, and over 60 strainsevaluated by the inventor, all exhibit a marked decrease in omega-3highly unsaturated fatty acids as a percentage of total fatty acids,when undergoing nitrogen limitation (Erwin, 1973; Pohl & Zurheide,1979).

With respect to economics and to utilizing omega-3 highly unsaturatedfatty acids as a food additive, it would be desirable to produce thesefatty acids in a heterotrophic culture. Heterotrophy is the capacity forsustained and continuous growth and cell division in the dark in whichboth energy and cell carbon are obtained solely from the metabolism ofan organic substrate(s). Since light does not need to be supplied to aheterotrophic culture, the cultures can be grown at very high densitiesin closed reactors. Heterotrophic organisms are those which obtainenergy and cell carbon from organic substrates, and are able to grow inthe dark. Heterotrophic conditions are those conditions that permit thegrowth of heterotrophic organisms, whether light is present or not.However, the vast majority of algae are predominantly photoautotrophic,and only a few types of heterotrophic algae are known. U.S. Pat. Nos.3,142,135 and 3,882,635 describe processes for the heterotrophicproduction of protein and pigments from algae such as Chlorella,Spongiocuccum, and Prototheca. However these genera and others that havebeen documented to grow very well heterotrophically (e.g. Scenedesmus),do not produce omega-3 highly unsaturated fatty acids (Erwin, 1973). Thevery few heterotrophic algae known to produce any omega-3 highlyunsaturated fatty acids (e.g., apochlorotic diatoms or apochloroticdinoflagellates) generally grown slowly and produce low amounts ofomega-3 highly unsaturated fatty acids as a percentage of ash-free dryweight (Harrington and Holtz, 1968; Tornabene et al., 1974).

A few higher fungi are known to produce omega-3 highly unsaturated fattyacids, but they comprise only a very small fraction of the total fattyacids in the cells (Erwin, 1973; Wassef, 1977; Weete, 1980). As such,they would not be good candidates for commercial production of omega-3highly unsaturated fatty acids. For example, Yamada et al. (1987)recently reported on the cultivation of several species of the fungus,Mortierella, (isolated from soils) for the production of the omega-6fatty acid, arachidonic acid. These fungi also produce small amounts ofomega-3 eicosapentaenoic acid along with the arachidonic acid when grownat low temperatures (5°-24° C.). However, the resulting eicosapentaenoicacid content was only 2.6% of the dry weight of the cells, and the lowtemperatures necessary to stimulate production of this fatty acid inthese species would result in greatly decreased productivities (andeconomic potential) of the cultivation system. Some single-celledmembers of the order Thraustochytriales are also known to produceomega-3 highly unsaturated fatty acids (Ellenbogen, 1969, Wassef, 1977;Weete, 1980; Findlay et al.. 1986) but they are known to be difficult toculture. Sparrow (1960) noted that the minuteness and simple nature ofthe thalli of the family Thraustochytriaceae (order Thraustochytriales)make them exceedingly difficult to propagate. Additional reasons forthis difficulty have been outlined by Emerson (1950) and summarized bySchneider (1976): "1) these fungi consist of very small thalli of onlyone or a few cells, which generally grow very slowly in culture, and arevery sensitive to environmental perturbation; 2) they are generallysaprophytes, or parasites with very specialized nutritional andenvironmental demands; and 3) in pure culture they generally exhibitrestricted growth, with vegetative growth terminating after a fewgenerations." (Although some prior art classifies the thraustochytridsas fungi, the most recent consensus is that they should be classified asalgae, see discussion below.)

As a result little attention has been paid to the numerous orders ofthese microorganisms, and those studies that have been conducted, havebeen predominantly carried out with a taxonomic or ecological focus. Forexample, even though the simple fatty acid distribution of severalmembers of the order Thraustochytriales has been reported from ataxonomic perspective (Ellenbogen, 1969); Findlay et al.. 1986), no onehas ever reported their total fatty acid content or lipid content aspercent dry weight. Unless data on the total lipid content is available,one cannot evaluate an organism's potential for use in the production ofany type of fatty acid. For example, the omega-3 highly unsaturatedfatty acid content of the lipids of some marine macroalgae (seaweeds) isreported to be very high, up to 51% of total fatty acids (Pohl &Zurheide, 1979). However, the lipid content of macroalgae is typicallyvery low, only 1-2% of cellular dry weight (Ryther, 1983). Therefore,despite the reported high content of omega-3 highly unsaturated fattyacids in the fatty acids of macroalgae, they would be considered to bevery poor candidate organisms for the production of omega-3 highlyunsaturated fatty acids. Despite a diligent search by the inventor, noreports of simple proximate analysis (% protein, carbohydrate and lipid)of the Thraustochytriales has been found, nor has anyone reportedattempts to cultivate these species for purposes other than laboratorystudies of their taxonomy, physiology or ecology. Additionally, many ofthe strains of these microorganisms have been isolated by simple pollenbaiting techniques (e.g., Gaertner, 1968). Pollen baiting techniques arevery specific for members of the Thraustochytriales, but do not selectfor any characteristics which may be desirable for large scalecultivation of microorganisms.

Thus, until the present invention, there have been no knownheterotrophic organisms suitable for culture that produce practicallevels of omega-3 highly unsaturated fatty acids and such organisms havebeen thought to be very rare in the natural environment.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed toward a food product with a highconcentration of omega-3 highly unsaturated fatty acids (HUFAs) whichincludes microorganisms characterized by having a high concentration offatty acids of which a high percentage are omega-3 highly unsaturatedfatty acids. In addition or alternatively, the food product can includeomega-3 HUFAs extracted from the microorganisms. Specifically, themicroorganisms are Thraustochytriales, namely, Thraustochytrium orSchizochytrium. The microorganisms or extracted omega-3 HUFAs areincorporated with additional food material which may be either animalfood or human food. The food product of the present invention may havethe bioavailability of the omega-3 HUFAs contained therein increased bylysing the cells of the microorganisms. The food product may also beextruded. In order to prevent degradation of the omega-3 HUFAs, the foodproduct may be packaged under non-oxidizing conditions or may furthercomprise an antioxidant.

Another embodiment of the present invention relates to a method ofraising an animal comprising feeding the animal Thraustochytriales oromega-3 HUFAs extracted therefrom. Animals raised by the method of thepresent invention include poultry, cattle, swine and seafood, whichincludes fish, shrimp and shellfish. The omega-3 HUFAs are incorporatedinto the flesh, eggs and other products of these animals which areconsumed by humans.

Omega-3 HUFAs may be consumed as the whole cell microbial product, theextracted omega-3 HUFA product, or the animal or animal productincorporating omega-3 HUFAs. Increased intake of omega-3 HUFAs producedin accordance with the present invention by humans is effective inpreventing or treating cardiovascular diseases, inflammatory and/orimmunological diseases, and cancer.

Yet another embodiment of the present invention is a method of producingomega-3 HUFAs which comprises culturing Thraustochytriales in a mediumwith a source of organic carbon and assimilable nitrogen. Preferably,the source of organic carbon and assimilable nitrogen comprises groundgrain. The method further comprises culturing Thraustochytrialesconsisting of Thraustochytrium, Schizochytrium, or mixtures thereofunder nutrient-limited or nitrogen-limited conditions for an effectiveamount of time, preferably about 6 to about 24 hours, and harvesting theThraustochytriales during the period of nitrogen limitation in order toincrease the concentration of omega-3 HUFAs in the microorganisms. Themethod further comprises adding an antioxidant compound selected fromthe group consisting of BHT, BHA, TBHQ, ethoxyquin, beta-carotene,vitamin E and vitamin C during post-harvest processing in order toprevent degradation of the omega-3 HUFAs. The method further comprisesstressing the microorganisms with low temperatures during culturing,maintaining a high dissolved oxygen concentration in the medium duringculturing, and adding to the medium effective amounts of phosphorous anda microbial growth factor (yeast extract or corn steep liquor) toprovide sustained growth of the microorganisms. The present methodfurther includes culturing unicellular microorganisms having theidentifying characteristics of ATCC Nos. 20888, 20889, 20890, 20891,20892 and mutant strains derived therefrom. Omega-3 HUFAs produced bythe method can then be separated from the lipids extracted from themicroorganisms by fractional crystallization which comprises rupturingthe microorganism cells, extracting the lipid mixture from the rupturedcells with a solvent, hydrolyzing the lipid mixture, removingnon-saponifiable compounds and cold-crystallizing the non-HUFAs in thelipid mixture.

A further embodiment of the present invention is a method for selectingunicellular, aquatic microorganisms capable of heterotrophic growth andcapable of producing omega-3 HUFAs comprising selecting microorganismsof a size between about 1 μm and 25 μm from a small population ofmicroorganisms collected from naturally occuring shallow salinehabitats, culturing the microorganisms in a medium comprising organiccarbon, assimilable nitrogen, assimilable phosphorous and a microbialgrowth factor under heterotrophic conditions, and selecting clear,white, orange, or red-colored non-filamentous colonies having rough ortextured surfaces.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of definition throughout the application, it is understoodherein that a fatty acid is an aliphatic monocarboxylic acid. Lipids areunderstood to be fats or oils including the glyceride esters of fattyacids along with associated phosphatides, sterols, alcohols,hydrocarbons, ketones, and related compounds.

A commonly employed shorthand system is used in this specification todenote the structure of the fatty acids (e.g., Weete, 1980). This systemuses the letter "C" accompanied by a number denoting the number ofcarbons in the hydrocarbon chain, followed by a colon and a numberindicating the number of double bonds, i.e., C20:5, eicosapentaenoicacid. Fatty acids are numbered starting at the carboxy carbon. Positionof the double bonds is indicated by adding the Greek letter delta (Δ)followed by the carbon number of the double bond; i.e..C20:5omega-3Δ⁵,8,11,14,17. The "omega" notation is a shorthand systemfor unsaturated fatty acids whereby numbering from the carboxy-terminalcarbon is used. For convenience, w3 will be used to symbolize "omega-3,"especially when using the numerical shorthand nomenclature describedherein. Omega-3 highly unsaturated fatty acids are understood to bepolyethylenic fatty acids in which the ultimate ethylenic bond is 3carbons from and including the terminal methyl group of the fatty acid.Thus, the complete nomenclature for eicosapentaenoic acid, an omega-3highly unsaturated fatty acid, would be C20:5w3Δ⁵,8,11,14,17. For thesake of brevity, the double bond locations (Δ⁵,8,11,14,17) will beomitted. Eicosapentaenoic acid is then designated C20:5w3,Docosapentaenoic acid (C22:5w3Δ⁷,10,13,16,19) is C22:5w3, andDocosahexaenoic acid (C22:6w3Δ⁴,7,10,13,16,19) is C22:6w3. Thenonmenclature "highly unsaturated fatty acid" means a fatty acid with 4or more double bonds. "Saturated fatty acid" means a fatty acid with 1to 3 double bonds.

A collection and screening process was developed by the inventor toreadily isolate many strains of microorganisms with the followingcombination of economically desirable characteristics for the productionof omega-3 highly unsaturated fatty acids: 1) capable of heterotrophicgrowth; 2) high content of omega-3 highly unsaturated fatty acids; 3)unicellular; 4) preferably low content of saturated and omega-6 highlyunsaturated fatty acids; 5) preferably nonpigmented, white oressentially colorless cells; 6) preferably thermotolerant (ability togrow at temperatures above 30° C.); and 7) preferably euryhaline (ableto grow over a wide range of salinities, but especially at lowsalinities).

Collection, isolation and selection of large numbers of suitableheterotrophic strains can be accomplished by the following method.Suitable water samples and organisms typically can be collected fromshallow, saline habitats which preferably undergo a wide range oftemperature and salinity variation. These habitats include marine tidepools, estuaries and inland saline ponds, springs, playas and lakes.Specific examples of these collection sites are: 1) saline warm springssuch as those located along the Colorado river in Glenwood Springs,Colo., or along the western edge of the Stansbury Mountains, Utah; 2)playas such as Goshen playa located near Goshen, Utah; 3) marine tidepools such as those located in the Bird Rocks area of La Jolla, Calif.;and 4) estuaries, such as Tiajuana estuary, San Diego County, Calif.Special effort should be made to include some of the living plant matterand naturally occurring detritus (decaying plant and animal matter)along with the water sample. The sample can then be refrigerated untilreturn to the laboratory. Sampling error is minimized if the watersample is shaken for 15-30 seconds, prior to pipetting or pouring aportion, for example, 1-10 ml, into a filter unit. The filter unitincludes 2 types of filters: 1) on top, a sterile Whatman #4 filter(Trademark, Whatman Inc., Clifton, N.J.); and 2) underneath the Whatmanfilter, a polycarbonate filter with 1.0 μm pore size. The purpose of thefirst (top) filter is to remove all particulate matter greater thanabout 25 μm, generally allowing only unicellular type material to passonto the 1.0 μm polycarbonate filter. The first filter greatly reducesthe number of mold colonies that subsequently develop upon incubation ofthe polycarbonate filter at elevated temperatures, thereby enhancing theopportunities for other colonies to develop. Mold spores are verynumerous in coastal and inland saline waters, and mold colonies canquickly cover an agar plate unless screened out. The 1.0 μm size of thepolycarbonate filter is chosen to allow many of the bacteria to pass onthrough into the filtrate. The purpose of using a sandwich filter designis to select for unicellular organisms at least a portion of whose cellsrange in diameter from about 1 μm to about 25 μm in size (organismswhich could potentially be grown easily in a fermenter system forproduction on a large scale). Extensive growth of these unicellularorganisms can be encouraged by incubation of the polycarbonate filter onan agar plate. Competition between organisms growing on the filterfacilitates the isolation of competitive, robust strains ofsingle-celled microorganisms. Unicellular aquatic microorganismsselected by the foregoing method display a range of cell size dependingon growth conditions and stage of reproductive cycle. Most cells inculture have diameters in the range from about 1 μm to about 25 μm;however, cells (thalli and sporangia) in the cultures can be found thathave larger diameters (depending on the strain) up to about 60 μm.

After filtration, the polycarbonate filter can be placed on an agarplate containing saline media containing a source of organic carbon suchas carbohydrate including glucose, various starches, molasses, groundcorn and the like, a source of assimilable organic or inorganic nitrogensuch as nitrate, urea, ammonium salts, amino acids, microbial growthfactors included in one or more of yeast extract, vitamins, and cornsteep liquor, a source of assimilable organic or inorganic phosphorous,and a pH buffer such as bicarbonate. Microbial growth factors arecurrently unspecified compounds which enhance heterotrophic growth ofunicellular microorganisms, including fungi and algae. The agar platescan be incubated in the dark at 25°-35° C. (30° C. is preferred) andafter 2-4 days numerous colonies will have appeared on the filter.Recovery of 1-5 colonies/plate of the desired organism is not uncommon.Yeast colonies are distinguishable either by color (they frequently arepink) or by their morphology. Yeast colonies are smooth whereas thedesired organisms form in colonies with rough or textured surfaces.Individual cells of the desired organism can be seen through adissecting microscope at the colony borders, whereas yeast cells are notdistinguishable, due to their smaller size. Mold and higher fungicolonies are distinguishable from the desired organisms because they arefilamentous, whereas the desired organisms are non-filamentous. Clear orwhite-colored colonies can be picked from the plates and restreaked on anew plate of similar media composition. While most of the desiredorganisms are clear or white-colored, some are orange or red-colored dueto the presence of xanthophyll pigments and are also suitable forselection and restreaking. The new plate can be incubated under similarconditions, preferably at 30° C. and single colonies picked after a 2-4day incubation period. Single colonies can then be picked and placed in,for example, 50 ml of liquid medium containing the same organicenrichments (minus agar) as in the agar plates. These cultures can beincubated for 2-4 days at 30° C. with aeration, for example, on a rotaryshaker table (100-200 rpm.). When the cultures appear to reach maximaldensity, 20-40 ml of the culture can then be harvested by centrifugationor other suitable method and preserved, as by lyophilization. The samplecan then be analyzed by standard, well-known techniques including gaschromatography techniques to identify the fatty acid content of thestrain. Those strains with omega-3 highly unsaturated fatty acids canthereby be identified and cultures of these strains maintained forfurther screening.

Promising strains can be screened for temperature tolerance byinoculating the strains into 250 ml shaker flasks containing 50 ml ofculture media. These cultures are then incubated for 2 days on theshaker table over any desired temperature range from most practicallybetween 27°-48° C., one culture at each 3° C. interval. Production canbe quantified as the total amount of fatty acids produced per ml ofculture medium. Total fatty acids can be quantified by gaschromatography as described above. A similar process can also beemployed to screen for salinity tolerance. For salinity tolerance arange of salinities yielding conductivities from 5-40 mmho/cm isadequate for most purposes. Screening for the ability to utilize avariety of carbon and nitrogen sources can also be conducted employingthe procedure outlined above. The carbon and nitrogen sources wereevaluated herein at concentrations of 5 g/l. Carbon sources evaluatedwere: glucose, corn starch, ground corn, potato starch, wheat starch,and molasses. Nitrogen sources evaluated were: nitrate, urea, ammonium,amino acids, protein hydrolysate, corn steep liquor, tryptone, peptone,or casein. Other carbon and nitrogen sources can be used, the choicebeing open to those of ordinary skill in the art, based on criteria ofsignificance to the user.

It has been unexpectedly found that species/strains from the genusThrausochytrium can directly ferment ground, unhydrolyzed grain toproduce omega-3 HUFAs. This process is advantageous over conventionalfermentation processes because such grains are typically inexpensivesources of carbon and nitrogen. Moreover, practice of this process hasno detrimental effects on the beneficial characteristics of the algae,such as levels of omega-3 HUFAs.

The present process using direct fermentation of grains is useful forany type of grain, including without limitation, corn, sorghum, rice,wheat, oats, rye and millet. There are no limitations on the grind sizeof the grain. However, it is preferable to use at least coarsely groundgrain and more preferably, grain ground to a flour-like consistency.This process further includes alternative use of unhydrolyzed corn syrupor agricultural/fermentation by-products such as stillage, a wasteproduct in corn to alcohol fermentations, as an inexpensivecarbon/nitrogen source.

In another preferred process, it has been found that omega-3 HUFAs canbe produced by Thraustochytrium or Schizochytrium by fermentation ofabove-described grains and waste products which have been hydrolyzed.Such grains and waste products can be hydrolyzed by any method known inthe art, such as acid hydrolysis or enzymatic hydrolysis. A furtherembodiment is a mixed hydrolysis treatment. In this procedure, theground grain is first partially hydrolyzed under mild acid conditionsaccording to any mild acid treatment method known in the art.Subsequently, the partially hydrolyzed ground grain is furtherhydrolyzed by an enzymatic process according to any enzymatic processknown in the art. In this preferred process, enzymes such as amylase,amyloglucosidase, alpha or beta glucosidase, or a mixture of theseenzymes are used. The resulting hydrolyzed product is then used as acarbon and nitrogen source in the present invention.

Using the collection and screening process outlined above, strains ofunicellular fungi and algae can be isolated which have omega-3 highlyunsaturated fatty acid contents up to 32% total cellular ash-free dryweight (afdw), and which exhibit growth over a temperature range from15°-48° C. and grow in a very low salinity culture medium. Many of thevery high omega-3 strains are very slow growers. Strains which have beenisolated by the method outlined above, and which exhibit rapid growth,good production and high omega-3 highly unsaturated fatty acid content,have omega-3 unsaturated fatty acid contents up to approximately 10%afdw.

Growth of the strains by the invention process can be effected at anytemperature conducive to satisfactory growth of the strains, forexample, between about 15° C. and 48° C., and preferably between 25°-36°C. The culture medium typically becomes more alkaline during thefermentation if pH is not controlled by acid addition or buffers. Thestrains will grow over a pH range from 4.0-11.0 with a preferable rangeof about 5.5-8.5.

When growth is carried out in large vessels and tanks, it is preferableto produce a vegetative inoculum in a nutrient broth culture byinoculating this broth culture with an aliquot from a slant culture orculture preserved at -70° C. employing the cryoprotectantsdimethylsulfoxide (DMSO) or glycerol. When a young, active vegetativeinoculum has then been secured, it can be transferred aseptically tolarger production tanks or fermenters. The medium in which thevegetative inoculum is produced can be the same as, or different from,that utilized for the large scale production of cells, so long as a goodgrowth of the strain is obtained.

The inventor found that single-celled strains of the orderThraustochytriales (containing omega-3 fatty acids) isolated andscreened by the process outlined above, generally exhibited restrictedgrowth, with vegetative growth terminating after a few generations aspredicted by Emerson (1950) and Schneider (1976). However, the inventorfound that by maintaining relatively high concentrations of phosphorous(e.g., KH₂ PO₄ >0.2 g/l) and/or adding a nutritional supplement (sourceof fungal growth factors) such as yeast extract or corn steep liquor(greater than 0.2 g/l), continuously growing cultures of theseunicellular fungi could be maintained. The ability to maintain growthfor more than 2-3 generations in liquid culture is termed hereinsustained growth. As a group, strains in the genus Thraustochytriumappear to respond more favorably to phosphate additions than those inthe genus Schizochytrium, which appear to need less phosphate. In termsof nutritional supplements supplying fungal growth factors, corn steepliquor can be substituted for the yeast extract, and with some strains,has even a more enhanced effect for allowing the strains to achieve highdensities in culture. The corn steep liquor and yeast extract containone or more growth factors necessary for growth of the cells. While thegrowth factor(s) is not presently defined, it is a component of yeastextract and corn steep liquor, and either of these well-knownnutritional supplements are satisfactory. Carbon conversion efficienciesclose to 50% (g cell dry weight produced/100 g organic carbon added toculture medium) can easily be achieved employing this process.

A microbial product high in protein and high in omega-3 highlyunsaturated fatty acids can be produced by harvesting the cells in theexponential phase of growth. If a product significantly higher in lipidsand omega-3 highly unsaturated fatty acids is desired, the culture canbe manipulated to become nutrient limited, preferably, nitrogen limitedfor a suitable time, preferably in the range from 6 to 24 hours. Thecultures can be transferred to a nitrogen-free medium or, preferably,the initial nitrogen content of the growth medium can be provided suchthat nitrogen becomes depleted late in the exponential phase. Nitrogenlimitation stimulates total lipid production while maintaining highlevels of omega-3 highly unsaturated fatty acids as long as theinduction period is kept short, usually 6-24 hours. This phase of theculture, when the culture population has achieved its maximum celldensity, is known as the stationary phase. Length of the inductionperiod can be manipulated by raising or lowering temperature, dependingon the strain employed. Additionally, the cells can be cultured on acontinuous basis in a medium with a high carbon-to-nitrogen ratio,enabling continuous production of high lipid content (and high omega-3content) cellular biomass. The unicellular strains of heterotrophicmicroorganisms isolated by the screening procedure outlined above, tendto have high concentrations of three omega-3 highly unsaturated fattyacids: C20:5w3, C22:5w3 and C22:6w3 and very low concentration ofC20:4w6. The ratios of these fatty acids can vary depending on cultureconditions and the strains employed. Ratios of C20:5w3 to C22:6w3 canrun from about 1:1 to 1:30. Ratios of C22:5w3 to C22:6w3 can run from1:12 to only trace amounts of C22:5w3. In the strains that lack C22:5w3,the C20:5w3 to C 22:6w3 ratios can run from about 1:1 to 1:10. Anadditional highly unsaturated fatty acid, C22:5w6 is produced by some ofthe strains, including all of the prior art strains (up to a ratio of1:4 with the C22:6w3 fatty acid). However, C22:5w6 fatty acid isconsidered undesirable as a dietary fatty acid because it canretroconvert to the C20:4w6 fatty acid. The screening procedure outlinedin this invention, however, facilitates the isolation of some strainsthat contain no (or less than 1%) omega-6 highly unsaturated fatty acids(C20:4w6 or C22:5w6).

HUFAs in microbial products, such as those produced by the presentprocess, when exposed to oxidizing conditions can be converted to lessdesirable unsaturated fatty acids or to saturated fatty acids. However,saturation of omega-3 HUFAs can be reduced or prevented by theintroduction of synthetic antioxidants or naturally-occurringantioxidants, such as betacarotene, vitamin E and vitamin C, into themicrobial products.

Synthetic antioxidants, such as BHT, BHA, TBHQ or ethoxyquin, or naturalantioxidants such as tocopherols, can be incorporated into the food orfeed products by adding them to the products during processing of thecells after harvest. The amount of antioxidants incorporated in thismanner depends, for example, on subsequent use requirements, such asproduct formulation, packaging methods, and desired shelf life.

Concentrations of naturally-occurring antioxidants can be manipulated byharvesting a fermentation in stationary phase rather than duringexponential growth, by stressing a fermentation with low temperature,and/or by maintaining a high dissolved oxygen concentration in themedium. Additionally, concentrations of naturally occurring antioxidantscan be controlled by varying culture conditions such as temperature,salinity, and nutrient concentrations. Additionally, biosyntheticprecursors to vitamin E, such as L-tyrosine or L-phenylalanine, can beincorporated into fermentation medium for uptake and subsequentconversion to vitamin E. Alternatively, compounds which actsynergistically with antioxidants to prevent oxidation (e.g., ascorbicacid, citric acid, phosphoric acid) can be added to the fermentation foruptake by the cells prior to harvest. Additionally, concentrations oftrace metals, particularly those that exist in two or more valencystates, and that possess suitable oxidation-reduction potential (e.g.,copper, iron, manganese, cobalt, nickel) should be maintained at theminimum needed for optimum growth to minimize their potential forcausing autooxidation of the HUFAs in the processed cells.

Other products that can be extracted from the harvested cellular biomassinclude: protein, carbohydrate, sterols, carotenoids, xanthophylls, andenzymes (e.g., proteases). Strains producing high levels of omega-6fatty acids have also been isolated. Such strains are useful forproducing omega-6 fatty acids which, in turn, are useful startingmaterials for chemical synthesis of prostaglandins and othereicosanoids. Strains producing more than 25% of total fatty acids asomega-6 fatty acids have been isolated by the method described herein.

The harvested biomass can be dried (e.g., spray drying, tunnel drying,vacuum drying, or a similar process) and used as a feed or foodsupplement for any animal whose meat or products are consumed by humans.Similarly, extracted omega-3 HUFAs can be used as a feed or foodsupplement. Alternatively, the harvested and washed biomass can be useddirectly (without drying) as a feed supplement. To extend its shelflife, the wet biomass can be acidified (approximate pH 3.5-4.5) and/orpasteurized or flash heated to inactivate enzymes and then canned,bottled or packaged under a vacuum or non-oxidizing atmosphere (e.g., N₂or CO₂) The term "animal" means any organism belonging to the kingdomAnimalia. The term "animal" means any organism belonging to the kingdomAnimalia and includes, without limitation, any animal from which poultrymeat, seafood, beef, pork or lamb is derived. Seafood is derived from,without limitation, fish, shrimp and shellfish. The term "products"includes any product other than meat derived from such animals,including, without limitation, eggs or other products. When fed to suchanimals, omega-3 HUFAs in the harvested biomass or extracted omega-3HUFAs are incorporated into the flesh, eggs or other products of suchanimals to increase the omega-3 HUFA content thereof.

It should be noted that different animals have varying requirements toachieve a desired omega-3 HUFA content. For example, ruminants requiresome encapsulation technique for omega-3 HUFAs to protect theseunsaturated fatty acids from breakdown or saturation by the rumenmicroflora prior to digestion and absorption of the omega-3 HUFAs by theanimal. The omega-3 HUFA's can be "protected" by coating the oils orcells with a protein (e.g., zeain) or other substances which cannot bedigested (or are poorly digested) in the rumen. This allows the fattyacids to pass undamaged through the ruminant's first stomach. Theprotein or other "protectant" substance is dissolved in a solvent priorto coating the cells or oil. The cells can be pelleted prior to coatingwith the protectant. Animals having high feed conversion ratios (e.g.,4:1-6:1) will require higher concentrations of omega-3 HUFAs to achievedan equivalent incorporation of omega-3 HUFAs as animal with low feedconversion ratios (2:1-3:1). Feeding techniques can be further optimizedwith respect to the period of an animal's life that harvested biomass orextracted omega-3 HUFAs must be fed to achieve a desired result.

For most feed applications, the oil content of the harvested cells willbe approximately 25-50% afdw, the remaining material being protein andcarbohydrate. The protein can contribute significantly to thenutritional value of the cells as several of the strains that have beenevaluated have all of the essential amino acids and would be considereda nutritionally balanced protein.

In a preferred process, the freshly harvested and washed cells(harvested by belt filtration, rotary drum filtration, centrifugation,etc.) containing omega-3 HUFAs can be mixed with any dry ground grain inorder to lower the water content of the harvested cell paste to below40% moisture. For example, corn can be used and such mixing will allowthe cell paste/corn mixture to be directly extruded, using commonextrusion procedures. The extrusion temperatures and pressures can bemodified to vary the degree of cell rupture in the extruded product(from all whole cells to 100% broken cells). Extrusion of the cells inthis manner does not appear to greatly reduce the omega-3 HUFA contentof the cells, as some of the antioxidants in the grain may help protectthe fatty acids from oxidation, and the extruded matrix may also helpprevent oxygen from readily reaching the fatty acids. Synthetic ornatural antioxidants can also be added to the cell paste/grain mixtureprior to extrusion. By directly extruding the cell paste/grain mixture,drying times and costs can be greatly reduced, and it allowsmanipulation of the bioavailability of the omega-3 HUFAs for feedsupplement applications by degree of cell rupture. The desired degree ofcell rupture will depend on various factors, including the acceptablelevel of oxidation (increased cell rupture increases likelihood ofoxidation) and the required degree of bioavailability by the animalconsuming the extruded material.

The unicellular fungal strains isolated by the method described readilyflocculate and settle, and this process can be enhanced by adjusting thepH of the culture to pH ≦7.0. A 6-fold concentration of the cells within1-2 minutes can be facilitated by this process. The method can thereforebe employed to preconcentrate the cells prior to harvesting, or toconcentrate the cells to a very high density prior to nitrogenlimitation. Nitrogen limitation (to induce higher lipid production) cantherefore be carried out in a much smaller reactor, or the cells fromseveral reactors consolidated into one reactor.

A variety of procedures can be employed in the recovery of the microbialcells from the culture medium. In a preferred recovery process, thecells produced by the subject process are recovered from the culturemedium by separation by conventional means, such as by filtration orcentrifugation. The cells can then be washed; frozen, lyophilized, orspray dried; and stored under a non-oxidizing atmosphere of a gas suchas CO₂ or N₂ (to eliminate the presence of O₂), prior to incorporationinto a processed food or feed product.

Cellular lipids containing the omega-3 highly unsaturated fatty acidscan also be extracted from the microbial cells by any suitable means,such as by supercritical fluid extraction, or by extraction withsolvents such as chloroform, hexane, methylene chloride, methanol, andthe like, and the extract evaporated under reduced pressure to produce asample of concentrated lipid material. The omega-3 highly unsaturatedfatty acids in this preparation may be further concentrated byhydrolyzing the lipids and concentrating the highly unsaturated fractionby employing traditional methods such as urea adduction or fractionaldistillation (Schlenk, 1954), column chromatography (Kates, 1986), or bysupercritical fluid fractionation (Hunter, 1987). The cells can also bebroken or lysed and the lipids extracted into vegetable or other edibleoil (Borowitzka and Borowitzka, 1988). The extracted oils can be refinedby well-known processes routinely employed to refine vegetables oils(e.g. chemical refining or physical refining). These refining processesremove impurities from extracted oils before they are used or sold asedible oils. The refining process consists of a series of processes todegum, bleach, filter, deodorize and polish the extracted oils. Afterrefining, the oils can be used directly as a feed or food additive toproduce omega-3 HUFA enriched products. Alternatively, the oil can befurther processed and purified as outlined below and then used in theabove applications and also in pharmaceutical applications.

In a preferred process, a mixture of high purity omega-3 HUFAs or highpurity HUFAs can be easily concentrated from the extracted oils. Theharvested cells (fresh or dried) can be ruptured or permeabilized bywell-known techniques such as sonication, liquid-shear disruptionmethods (e.g., French press of Manton-Gaulin homogenizer), bead milling,pressing under high pressure, freeze-thawing, freeze pressing, orenzymatic digestion of the cell wall. The lipids from the ruptured cellsare extracted by use of a solvent or mixture of solvents such as hexane,chloroform, ether, or methanol. The solvent is removed (for example by avacuum rotary evaporator, which allows the solvent to be recovered andreused) and the lipids hydrolyzed by using any of the well-known methodsfor converting triglycerides to free fatty acids or esters of fattyacids including base hydrolysis, acid hydrolysis, or enzymatichydrolysis. The hydrolysis should be carried out at as low a temperatureas possible (e.g., room temperature to 60° C.) and under nitrogen tominimize breakdown of the omega-3 HUFAs. After hydrolysis is completed,the nonsaponifiable compounds are extraced into a solvent such as ether,hexane or chloroform and removed. The remaining solution is thenacidified by addition of an acid such as HCl, and the free fatty acidsextracted into a solvent such as hexane, ether, or chloroform. Thesolvent solution containing the free fatty acids can then be cooled to atemperature low enough for the non-HUFAs to crystallize, but not so lowthat HUFAs crystallize. Typically, the solution is cooled to betweenabout -60° C. and about -74° C. The crystallized fatty acids (saturatedfatty acids, and mono-, di-, and tri-enoic fatty acids) can then beremoved (while keeping the solution cooled) by filtration,centrifugation or settling. The HUFAs remain dissolved in the filtrate(or supernatant). The solvent in the filtrate (or supernatant) can thenbe removed leaving a mixture of fatty acids which are >90% purity ineither omega-3 HUFAs or HUFAs which are greater than or equal to 20carbons in length. The purified omega-3 highly unsaturated fatty acidscan then be used as a nutritional supplement for humans, as a foodadditive, or for pharmaceutical applications. For these uses thepurified fatty acids can be encapsulated or used directly. Antioxidantscan be added to the fatty acids to improve their stability.

The advantage of this process is that it is not necessary to go throughthe urea complex process or other expensive extraction methods, such assupercritical CO₂ extraction or high performance liquid chromatography,to remove saturated and mono-unsaturated fatty acids prior to coldcrystallization. This advantage is enabled by starting the purificationprocess with an oil consisting of a simple fatty acid profile such asthat produced by Thraustochytrids (3 or 4 saturated or monounsaturatedfatty acids with 3 or 4 HUFAs, two groups of fatty acids widelyseparated in terms of their crystallization temperatures) rather than acomplex oil such as fish oil with up to 20 fatty acids (representing acontinuous range of saturated, mono-, di-, tri-, and polyenoic fattyacids, and as such, a series of overlapping crystallizationtemperatures).

In a preferred process, the omega-3 HUFA enriched oils can be producedthrough cultivation of strains of the genus Thraustochytrium. After theoils are extracted from the cells by any of several well-known methods,the remaining extracted (lipids removed) biomass which is comprisedmainly of proteins and carbohydrates, can be sterilized and returned tothe fermenter, where the strains of Thraustochytrium can directlyrecycle it as a nutrient source (source of carbon and nitrogen). Noprehydrolysis or predigestion of the cellular biomass is necessary.Extracted biomass of the genus Schizochytrium can be recycled in asimilar manner if it is first digested by an acid and/or enzymatictreatment.

As discussed in detail above, the whole-cell biomass can be useddirectly as a food additive to enhance the omega-3 highly unsaturatedfatty acid content and nutritional value of processed foods for humanintake or for animal feed. When used as animal feed, omega-3 HUFAs areincorporated into the flesh or other products of animals. The complexlipids containing these fatty acids can also be extracted from thewhole-cell product with solvents and utilized in a more concentratedform (e.g., encapsulated) for pharmaceutical or nutritional purposes andindustrial applications. A further aspect of the present inventionincludes introducing omega-3 HUFAs from the foregoing sources intohumans for the treatment of various diseases. As defined herein, "treat"means both the remedial and preventative practice of medicine. Thedietary value of omega-3 HUFAs is widely recognized in the literature,and intake of omega-3 HUFAs produced in accordance with the presentinvention by humans is effective for treating cardiovascular diseases,inflammatory and/or immunological diseases and cancer.

The present invention will be described in more detail by way of workingexamples. Species meeting the selection criteria described above havenot been described in the prior art. By employing these selectioncriteria, the inventor isolated over 25 potentially promising strainsfrom approximately 1000 samples screened. Out of the approximate 20,500strains in the American Type Culture Collection (ATCC), 10 strains werelater identified as belonging to the same taxonomic group as the strainsisolated by the inventor. Those strains still viable in the Collectionwere procured and used to compare with strains isolated and cultured bythe disclosed procedures. The results of this comparison are presentedin Examples 5 and 6 below.

Since the filing of the parent case, recent developments have resultedin revision of the taxonomy of the Thraustochytrids. The most recenttaxonomic theorists place them with the algae. However, because of thecontinued taxonomic uncertainty, it would be best for the purposes ofthe present invention to consider the strains as Thraustochydrids(Order: Thraustochytriales; Family: Thraustochytriaceae; Genus:Thraustochytrium or Schizochytrium). The most recent taxonomic changesare summarized below.

All of the strains of unicellular microorganisms disclosed and claimedherein are members of the order Thraustochytriales. Thraustochytrids aremarine eukaryotes with a rocky taxonomic history. Problems with thetaxonomic placement of the Thraustochytrids have been reviewed mostrecent by Moss (1986), Bahnweb and Jackle (1986) and Chamberlain andMoss (1988). For convenience purposes, the Thraustochytrids were firstplaced by taxonomists with other colorless zoosporic eukaryotes in thePhycomycetes (algae-like fungi). The name Phycomycetes, however, waseventually dropped from taxonomic status, and the Thraustochytridsretained in the Oomycetes (the biflagellate zoosporic fungi). It wasinitially assumed that the Oomycetes were related to the heterokontalgae, and eventually a wide range of ultrastructural and biochemicalstudies, summarized by Barr (1983) supported this assumption. TheOomycetes were in fact accepted by Leedale (1974) and other phycologistsas part of the heterokont algae. However, as a matter of convenienceresulting from their heterotrophic nature, the Oomycetes andThraustochytrids have been largely studied by mycologists (scientistswho study fungi) rather than phycologists (scientists who study algae).

From another taxonomic perspective, evolutionary biologists havedeveloped two general schools of thought as to how eukaryotes evolved.One theory proposes an exogenous origin of membrane-bound organellesthrough a series of endosymbioses (Margulis (1970); e.g., mitochondriawere derived from bacterial endosymbionts, chloroplasts fromcyanophytes, and flagella from spirochaetes). The other theory suggestsa gradual evolution of the membrane-bound organelles from thenon-membrane-bounded systems of the prokaryote ancestor via anautogenous process (Cavalier-Smith 1975). Both groups of evolutionarybiologists however, have removed the Oomycetes and Thraustachytrids fromthe fungi and place them either with the chromophyte algae in thekingdom Chromophyta (Cavalier-Smith 1981) or with all algae in thekingdom Protoctista (Margulis and Sagan (1985).

With the development of electron microscopy, studies on theultrastructure of the zoospores of two genera of Thraustochytrids,Thraustochytrium and Schizochytrium. (Perkins 1976; Kazama 1980; Barr1981) have provided good evidence that the Thraustochytriaceae are onlydistantly related to the Oomycetes. Additionally, more recent geneticdata representing a correspondence analysis (a form of multivariatestatistics) of 5S ribosomal RNA sequences indicate thatThraustochytriales are clearly a unique group of eukaryotes, completelyseparate from the fungi, and most closely related to the red and brownalgae, and to members of the Oomycetes (Mannella et al. 1987). Recentlyhowever, most taxonomists have agreed to remove the Thraustochytridsfrom the Oomycetes (Bartnicki-Garcia 1988).

In summary, employing the taxonomic system of Cavalier-Smith (1981,1983), the Thraustochytrids are classified with the chromophyte algae inthe kingdom Chromophyta, one of the four plant kingdoms. This placesthem in a completely different kingdom from the fungi, which are allplaced in the kingdom Eufungi. The taxonomic placement of theThraustochytrids is therefore summarized below:

Kingdom: Chromophyta

Phylum: Heterokonta

Order: Thraustochytriales

Family: Thraustochytriaceae

Genus: Thraustochytrium or Schizochytrium

Despite the uncertainty of taxonomic placement within higherclassifications of Phylum and Kingdom, the Thraustochytrids remain adistinctive and characteristic grouping whose members remainclassifiable within the order Thraustochytriales.

Omega-3 highly unsaturated fatty acids are nutritionally important fattyacids for both humans and animals. Currently the only commerciallyavailable source of these fatty acids is from fish oil. However, thereare several significant problems with the use of fish oil as a food orfeed additive or supplement. First and most significantly, fish oilshave a strong fishy taste and odor, and as such cannot be added toprocessed foods as a food additive, without negatively affecting thetaste of the food product. This is also true for many of itsapplications as an animal food or feed additive. For example,experiments by the inventor and others have indicated that laying hensreadily go off their feed when fed for more than a few days on feedenriched with fish oils. Fish oils are very unstable, easily becomingrancid and thereby decreasing the palatability and nutritional value offeed.

Secondly, fish oils generally only contain 20-30% omega-3 HUFAs.Desirable omega-3 HUFA contents in marine larval fish and shrimp feedscan be as high as 5-10% of their dry weight. To constitute anappropriate synthetic diet containing 5-10% omega-3 HUFAs could requirea diet of 15-30% fish oil. Such a synthetic diet would not be the mostsuitable for these larval organisms either in terms of palatability,digestibility, or stability (Sargent et al. (1989). In terms of humannutrition, the other 70-80% of fatty acids in fish oil are saturated andomega-6 fatty acids, fatty acids which can have deleterious healtheffects for humans. Processes for the isolation of pure omega-3 fattyacids from fish oils are involved and expensive, resulting in very highprices ($200-$1000/ g) for pure forms of these fatty acids, much tooexpensive for use as a food or feed additive (Sigma Chemical, Co., 1988;CalBiochem Co., 1988).

Third, most feeds currently used by the aquaculture industry are grainbased feeds, and as such, are relatively low in omega-3 HUFA content.Recent surveys of seafood products have demonstrated that fish andshrimp produced by aquaculture farms generally only have 1/3-1/2 theomega-3 HUFA content of wild caught fish and shrimp (Pigott 1989). Foraquacultured organisms, many which are prized because of their mild,non-fishy taste, increasing the fish oil content of their food is noteffective, because it results in a fish-tasting product.

As a result of the problems described above, there is an important needfor development of alternative (non-fish based) sources of omega-3HUFAs.

The microbial product of the present invention can be used as a food orfeed supplement to provide an improved source of omega-3 highlyunsaturated fatty acids which has significant advantages overconventional sources. Poultry fed a diet supplemented with the microbialproduct incorporate the omega-3 highly unsaturated fatty acids into bodytissues and into eggs. The eggs exhibit no fishy odor or taste, nochange in yolk color. The poultry do not stop eating the supplementedfeed, as they do with fish oil-supplemented feed. Feed supplemented withthe microbial product of the present invention has a normal shelf lifeand does not become rancid upon standing at room temperature for severaldays. The eggs and flesh of poultry fed according to the invention areuseful in human nutrition as sources of omega-3 highly unsaturated fattyacids, yet are low in omega-6 fatty acid content and lack a fishyflavor.

The microbial product of the present invention is also of value as asource of omega-3 highly unsaturated fatty acids for fish, shrimp andother products produced by aquaculture. The product can be addeddirectly as a supplement to the feed or it can be fed to brine shrimp orother live feed organisms intended for consumption by the aquaculturedproduct. The use of such supplement enables the fish or shrimp farmer tobring to market an improved product retaining the taste advantagesprovided by aquaculture but having the high omega-3 highly unsaturatedfatty acid content of wild caught fish coupled to the additional healthadvantage of reduced omega-6 fatty acid content.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a bar graph showing the effects of various media supplementson fatty acid yield, using Thraustochytrium sp. UT42-2 (ATCC No. 20891),a strain isolated according to the selection method of the invention asa test strain. The experimental procedure is described in Example 2.Ordinate: fatty acid yield, normalized to control, FFM media withoutsupplements. Abscissa: specific additions, 1) 2x "B"-vitamin mix; 2) "A"vitamin mix; 3) 2x PI metals; 4) 28 mg/1 KH₂ PO₄ ; 5) treatments 2), 3)and 4) combined; and 6) 480 mg/1 KH₂ PO₄.

FIG. 2 is a graphical representation of highly unsaturated fatty acidproduction in newly isolated strains of the invention, represented by □and previously isolated strains represented by +. Each point representsa strain, the position of each point is determined by the percent byweight of total fatty acids which were omega-3 highly unsaturated fattyacids (abscissa) and the percent by weight of total fatty acids whichwere omega-6 fatty acids (ordinate). Only those strains of the inventionwere plotted wherein less than 10.6% (w/w) of total fatty acids wereomega-6 and more than 67% of total fatty acids were omega-3. Data fromTable 4.

FIG. 3 is a graphical representation of highly unsaturated fatty acidproduction in newly isolated strains of the invention, represented by □and previously isolated strains, represented by +. Each point representsa strain, the position of each point is determined by the percent byweight of total fatty acids which were omega-3 highly unsaturated fattyacids (abscissa) and percent of weight of total fatty acids which wereeicosapentaenoic acid (EPA C20:5w3) (ordinate). Only those strains ofthe invention were plotted wherein more than 67% (w/w) of total fattyacids were omega-3 and more than 7.8% (w/w) of total fatty acids wereC20:5w3.

FIG. 4 is a graphical representation of omega-3 highly unsaturated fattyacid composition in newly isolated strains of the invention, representedby □, and previously isolated strains, represented by +. Each pointrepresents a separate strain. Values on the abscissa are weight fractionof total omega-3 highly unsaturated fatty acids which were C20:5w3 andon the ordinate are weight fraction of total omega-3 fatty highlyunsaturated acids which were C22:6w3. Only strains of the invention wereplotted having either a weight fraction of C20:5w3 28% or greater, or aweight fraction of C22:6w3 greater than 93.6%.

FIG. 5 is a graph showing growth of various newly isolated strains ofthe invention and previously isolated strains, at 25° C. and at 30° C.Growth rates are normalized to the growth rate of strain U-30 at 25° C.Previously isolated strains are designated by their ATCC accessionnumbers. Numerical data in terms of cell number doublings per day aregiven in Table 5.

FIG. 6 is a graph of total yields of cellular production after inductionby nitrogen limitation. Each of ash-free dry weight, total fatty acidsand omega-3 highly unsaturated fatty acids, as indicated, was plotted,normalized to the corresponding value for strain 28211. All strains areidentified by ATCC accession numbers.

FIG. 7 is a graph of fatty acid yields after growth in culture mediahaving the salinity indicated on the abscissa. Strains shown are newlyisolated strains S31 (ATCC 20888) (□) and U42-2 (ATCC 20891) (+) andpreviously isolated strains, ATCC 28211 and ATCC 28209 (Δ). Fatty acidyields are plotted was relative yields normalized to an arbitrary valueof 1.00 based on the average growth rate exhibited by S31 (ATCC 20888)(□) over the tested salinity range.

FIG. 8 is a graph of increases in the omega-3 highly unsaturated fattyacid content of the total lipids in the brine shrimp, Artemia salina,fed Thraustochytrid strain (ATCC 20890) isolated by the method inExample 1. EPA =C20:5w3; DHA =C22:6w3.

FIG. 9 is a graph of increases in the omega-3 highly unsaturated fattyacid content of the total lipids in the brine shrimp, Artemia salina,fed Thraustochytrid strain (ATCC 20888) isolated by the method inExample 1. EPA =C20:5w3; DHA =C22:6w3.

EXAMPLES Example 1. Collection and Screening

A 150 ml water sample was collected from a shallow, inland saline pondand stored in a sterile polyethylene bottle. Special effort was made toinclude some of the living plant material and naturally occurringdetritus (decaying plant and animal matter) along with the water sample.The sample was placed on ice until return to the laboratory. In the lab,the water sample was shaken for 15-30 seconds, and 1-10 ml of the samplewas pipetted or poured into a filter unit containing 2 types offilters: 1) on top, a sterile 47 mm diameter Whatman #4 filter having apore size about 25 μm; and 2) underneath the Whatman filter, a 47 mmdiameter polycarbonate filter with about 1.0 μm pore size. Given slightvariations of nominal pore sizes for the filters, the cells collected onthe polycarbonate filter range in size from about 1.0 μm to about 25 μm.

The Whatman filter was removed and discarded. The polycarbonate filterwas placed on solid F-1 media in a petri plate, said media consisting of(per liter): 600 ml seawater (artificial seawater can be used), 400 mldistilled water, 10 g agar, 1 g glucose, 1 g protein hydrolysate, 0.2 gyeast extract, 2 ml 0.1 M KH₂ PO₄, 1 ml of a vitamin solution (A-vits)(Containing 100 mg/l thiamine, 0.5 mg/l biotin, and 0.5 mg/lcyanocobalamin), b 5 ml of a trace metal mixture (PII metals, containingper liter: 6.0 g Na₂ EDTA, 0.29 g FeCl₃ 6H₂ O, 6.84 g H₃ BO₃, 0.86 MnCl₂4H₂ O, 0.06 g ZnCl₂, 0.026 g CoCl₂ 6H₂ O, (0.052 g NiSO₄ H=hd 2O, 0.002g CuSo₄ 5H₂ O, and 0.005 g Na₂ MoO₄ 2H₂ O, and 500 mg each ofstreptomycin sulfate and peniocillin-G. The agar plate was incubated inthe dark at 30° C. After 2-4 days numerous colonies appeared on thefilter. Colonies of unicellular fungi (except yeast) were picked fromthe plate and restreaked on a new plate of similar media composition.Special attention was made to pick all colonies consisting of colorlessor white cells. The new plate was incubated at 30° C. and singlecolonies picked after a 2-4 day incubation period. Single colonies werethen picked and placed in 50 ml of liquid medium containing the sameorganic enrichments as in the agar plates. These cultures were incubatedfor 2≧4 days at 30° C. on a rotary shaker table (100-200 rpm). When thecultures appeared to reach maximal density, 20-40 ml of the culture washarvested, centrifuged and lyphilized. The sample was then analyzed bystandard, well-known gas chromatographic techniques (e.g., Lepage andRoy, 1984) to identify the fatty acid content of the strain. Thosestrains with omega-3 highly unsaturated fatty acids were therebyidentified, and cultures of these strains were maintained for furtherscreening.

Using the collection and screening process outlined above, over 150strains of unicellular fungi have been isolated which have omega-3highly unsaturated fatty acid contents up to 32% total cellular ash-freedry weight, and which exhibit growth over a temperature range from15-48° C. Strains can also be isolated which have less than 1% (as % oftotal fatty acids) of the undesirable C20:4w6 and C22:5w6 highlyunsaturated fatty acids. Strains of these fungi can be repeatedlyisolated from the same location using the procedure outlined above. Afew of the newly isolated strains have very similar fatty acid profiles.The possibility that some are duplicate isolates of the same straincannot be ruled out at present. Further screening for other desirabletraits such as salinity tolerance or ability to use a variety of carbonand nitrogen sources can then be carried out using a similar process.

Example 2. Maintaining unrestricted cell growth: phosphorus

Cells of Thraustochytrium sp. U42-2 (ATCC No. 20891), a strain isolatedby the method in Example 1, were picked from solid F-medium andinoculated into 50 ml of modified FFM medium (Fuller et al., 1964). Thismedium containing: seawater, 1000 ml; glucose, 1.0 g; gelatinhydrolysate, 1.0 g; liver extract, 0.01 g; yeast extract, 0.1 g; PIImetals, 5 ml; 1 ml B-vitamins solution (Goldstein et al., 1969); and 1ml of an antibiotic solution (25 g/l streptomycin sulfate andpenicillin-G). 1.0 ml of the vitamin mix (pH 7.2) contains: thiamineHC1, 200 μg; biotin, 0.5 μg; cyanocobalamin, 0.05 μg; nicotinic acid,100 μg; calcium pantothenate, 100 μg; riboflavin, 5.0 μg; pyridoxineHC1, 40.0 μg; pyridoxamine 2HC1, 10.0 μg; p-aminobenzoic acid, 10 μg;chlorine HC1, 500 μg; inositol, 1.0 mg; thymine, 0.8 mg; orotic acid,0.26 mg; folinic acid, 0.2 μg; and folic acid, 2.5 μg. 250 ml erlenmeyerflasks with 50 ml of this medium were placed on an orbital shaker (200rpm) at 27° C. for 2-4 days, at which time the culture had reached theirhighest densities. One ml of this culture was transferred to a new flaskof modified FFM medium, with the extra addition of one of the followingtreatments on a per liter basis: 1) 1 ml of the B-vitamin mix; 2) 1 mlof A-vitamin solution; 3) 5 ml PII Metals; 4) 2 ml of 0.1 M KH₂ PO₂ (≈28mg); 5) treatments 2, 3, and 4 combined; and 6) 480 mg KH₂ PO₄. One mlof the culture was also transferred to a flask of modified FFM mediumwhich had no extra additions made to it and served as a control for theexperiment. The cultures were incubated for 48 hr. at 27° C. on a rotaryshaker (200 rpm). The cells were then harvested by centrifugation andthe fatty acids were quantified by gas chromatography. The results areillustrated in FIG. 1 and Table 1. In FIG. 1, the yields are plotted asratios of the control, whose relative yield is therefore 1.0. Treatments1-6 are as follows: 1) 2x concentration of B vitamins; 2) 2xconcentration of A vitamins; 3) 2x concentration of trace metals; 4) 2xconcentration of (B vitamins+phosphate+trace metals); 5) 2xconcentration of phosphate; and 6) 24 mg phosphate per 50 ml (0.48 g perliter). Only the treatment of adding 0.48 g KH₂ OP₄ per liter resultedin enhanced growth and resulted in significantly increased fatty acidyield.

                  TABLE 1                                                         ______________________________________                                        Effect of various nutrient additions on the                                   yield of fatty acids in Thraustochytrium sp.                                  U42-2 (ATCC No. 20891)                                                                              Fatty Acid Yield                                        Treatment             mg/liter                                                ______________________________________                                        Control               23                                                      2 × concentration of B vitamin mix                                                            17                                                      2 × concentration of A vitamin mix                                                            24                                                      2 × concentration trace metals                                                                27                                                      2 × concentration B vitamin mix,                                                              24                                                      2 × PO.sub.4 and 2 × concentration trace                          metals                                                                        2 × concentration PO.sub.4                                                                    23                                                      24 mg phosphate per 50 ml                                                                           45                                                      ______________________________________                                    

Example 3. Maintaining unrestricted growth: PO₄ and yeast extract

Cells of Schizochytrium aggregatum (ATCC 28209) were picked from solidF-1 medium and inoculated into 50 ml of FFM medium. The culture wasplaced on a rotary shaker (200 rpm) at 27° C. After 3-4 days, 1 ml ofthis culture was transferred to 50 ml of each of the followingtreatments: 1) FFM medium (as control); and 2) FFM medium with theaddition of 250 mg/1 KH2PO₄ and 250 mg/1 yeast extract. These cultureswere placed on a rotary shaker (200 rpm) at 27° C. for 48 hr. The cellswere harvested and the yield of cells quantified. In treatment 1, thefinal concentration of cells on an ash-free dry weight basis was 616mg/l. In treatment 2, the final concentration of cells was 1675 mg/l,demonstrating the enhanced effect of increasing PO₄ and yeast extractconcentrations in the culture medium.

Example 4. Maintaining unrestricted growth: substitution of corn steepliquor for yeast extract

Cells of Schizochytrium sp. S31 (ATCC No. 20888) were picked from solidF-1 medium and placed into 50 ml of M-5 medium. This medium consists of(on a per liter basis): NaCl, 25 g; MgSO₄.7H₂ O, 5 g; KCl, 1 g; CaCl₂,200 mg; glucose, 5 g; glutamate, 5 g; KH₂ PO₄, 1 g; PII metals, 5 ml;A-vitamins solution, 1 ml; and antibiotic solution, 1 ml. The pH of thesolution was adjusted to 7.0 and the solution was filter sterilized.Sterile solutions of corn steep liquor (4 g/40 ml; pH 7.0) and yeastextract 1 g/40 ml; pH 7.0) were prepared. To one set of M-5 mediumflasks, the following amount of yeast extract solution was added: 1) 2ml; 2) 1.5 ml; 3) 1 ml; 4) 0.5 ml; and 5) 0.25 ml. To another set of M-5medium flasks the yeast extract and corn steep liquor solutions wereadded at the following levels: 1) 2 ml yeast extract; 2) 1.5 ml yeastextract and 0.5 ml corn steep liquor; 3) 1.0 ml yeast extract and 1.0 mlcorn steep liquor; 4) 0.5 ml yeast extract and 1.5 ml corn steep liquor;and 5) 2 ml corn steep liquor. One ml of the culture in F-1 medium wasused to inoculate each flask. They were placed on a rotary shaker at 27°C. for 48 hr. The cells were harvested by centrifugation and the yieldof cells (as ash-free dry weight) was determined. The results are shownin Table 2. The results indicate the addition of yeast extract up to 0.8g/1 of medium can increase the yield of cells. However, addition of cornsteep liquor is even more effective and results in twice the yield oftreatments with added yeast extract. This is very advantageous for theeconomic production of cells as corn steep liquor is much less expensivethan yeast extract.

                  TABLE 2                                                         ______________________________________                                        Treatment                                                                     (Amount Nutrient    Ash-Free Dry Weight                                       Supplement Added)   (mg/l)                                                    ______________________________________                                         2.0 ml yeast ext.  4000                                                       1.5 ml yeast ext.  4420                                                       1.0 ml yeast ext.  4300                                                       0.5 ml yeast ext.  2780                                                      0.25 ml yeast ext.  2700                                                       2.0 ml yeast ext.  4420                                                       1.5 ml yeast ext. + 0.5 ml CSL*                                                                  6560                                                       1.0 ml yeast ext. + 1.0 ml CSL                                                                   6640                                                       0.5 ml yeast ext. + 1.5 ml CSL                                                                   7200                                                       2.0 ml CSL         7590                                                      ______________________________________                                         *CSL = corn steep liquor                                                 

Example 5. Enhanced highly unsaturated fatty acid content of strainsisolated by method in Example 1 compared to ATCC strains (previouslyknown strains)

A battery of 151 newly isolated strains, selected according to themethod described in Example 1, were sampled in late exponential phasegrowth and quantitatively analyzed for highly unsaturated fatty acidcontent by gas-liquid chromatography. All strains were grown either inMl medium or liquid FFM medium, whichever gave highest yield of cells.Additionally, five previously isolated Thraustochytrium orSchizochytrium species were obtained from the American Type CultureCollection, representing all the strains which could be obtained inviable form from the collection. These strains were: T. aureum (ATCC No.8211), T. aureum (ATCC No. 34304), T. roseum (ATCC No. 8210), T.straitum (ATCC No. 34473) and S. aggregatum (ATCC No. 28209). Thestrains all exhibited abbreviated growth in conventional media, andgenerally showed improved growth in media of the present invention,including M5 medium and FFM medium, Example 2. The fatty acidsproduction of each of the known strains was measured as described, basedupon the improved growth of the strains in media of the invention.

Fatty acid peaks were identified by the use of pure compounds of knownstructure. Quantitation, in terms of percent by weight of total fattyacids, was carried out by integrating the chromatographic peaks.Compounds identified were: palmitic acid (C16:0), C20:4w6 and C22:1(which were not resolved separately by the system employed), C20:5w3,C22:5w6, C22:5w3, and C22:6w3. The remainder, usually lower molecularweight fatty acids, were included in the combined category of "otherfatty acids." Total omega-3 fatty acids were calculated as the sum of20:5w3, 22:5w3 and 22:6w3. Total omega-6 fatty acids were calculated asthe sum of the 20:4/22:1 peak and the 22:5w6 peak.

The results are shown in Tables 3-4 and illustrated in FIGS. 2-4. FromTable 3 it can be seen that large numbers of strains can be isolated bythe method of the invention, and that large numbers of strainsoutperform the previously known strains by several important criteria.For example, 102 strains produced at least 7.8% by weight of total fattyacids C20:5w3, a higher percentage of that fatty acid than anypreviously known strain. Strains 23B (ATCC No. 20892) and 12B (ATCC No.20890) are examples of such strains. Thirty (30) strains of theinvention produced at least 68% by weight of total fatty acids asomega-3 fatty acids, more than any previously known strain. Strain 23B(ATCC No. 20892) is an example of such strains. Seventy-six (76) strainsof the invention yielded not more than 10% by weight of total fattyacids as omega-6 fatty acids, considered undesirable components of thehuman diet, lower than any previously known strain. Strains 23B (ATCCNo. 20892) and 12B (ATCC No. 20890) are examples of such strains. Inaddition, there are 35 strains of the invention that produce more than25% by weight of total fatty acids as omega-6 fatty acids, more than anypreviously known strain. While such strains may not be useful fordietary purposes, they are useful as feedstock for chemical synthesis ofeicosanoids starting from omega-6 fatty acids.

In addition, the data reveal many strains of the invention which producea high proportion of total omega-3 fatty acids as C22:6w3. In Table 4,48 of the strains shown in Table 2 were compared to the previously knownstrains, showing each of C20:5w3, C22:5w3 and C22:6w3 as percent byweight of total omega-3 content. Fifteen strains had at least 94% byweight of total omega-3 fatty acids as C22:6w3, more than any previouslyknown strain. Strain S8 (ATCC No. 20889) was an example of such strains.Eighteen strains had at least 28% by weight of total omega-3 fatty acidsas C20:5w3, more than any previously known strain. Strain 12B (ATCC No.20890) was an example of such strains.

FIG. 2 illustrates the set of strains, isolated by the method in Example1, that have more than 67% omega-3 fatty acids (as % of total fattyacids) and less than 10.6% omega-6 fatty acids (as % of total fattyacids). All of the previously known strains had less than 67% omega-3fatty acids (as % of total fatty acids) and greater than 10.6% omega-6(as % of total fatty acids).

FIG. 3 illustrates the set of strains, isolated by the method in Example1, that have more than 67% omega-3 fatty acids (as % of total fattyacids) and greater than 7.5% C20:5w3 (as % of total fatty acids). All ofthe previously known strains had less than 67% omega-3 fatty acids (as %of total fatty acids) and less than 7.8% C20:5w3 (as % of total fattyacids).

                                      TABLE 3                                     __________________________________________________________________________    PERCENT OF TOTAL FATTY ACIDS       Total                                                                              Total                                 C16:0                                                                             C20:4w6                                                                            C20:5w3                                                                            C22:5w6                                                                            C22:5w3                                                                            C22:6w3                                                                            Other FA                                                                            Omega 3                                                                            Omega 6                                                                            Strain                           __________________________________________________________________________    LIST OF STRAINS AND COMPOSITIONS UNDER STANDARD SCREENING CONDITIONS          30.4%                                                                             2.8% 6.6% 3.2% 0.2%  8.3%                                                                              48.5% 15.1%                                                                              6.0% 21                               22.9%                                                                             0.4% 2.3% 15.5%                                                                              0.5% 47.0%                                                                              11.5% 49.7%                                                                              15.9%                                                                              ATCC20889                        14.9%                                                                             6.5% 12.0%                                                                              11.8%                                                                              0.4% 49.7%                                                                              4.7%  62.1%                                                                              18.3%                                                                              U40-2                            40.3%                                                                             1.7% 3.8% 8.6% 0.0%  8.2%                                                                              37.4% 12.0%                                                                              10.2%                                                                              21B                              20.7%                                                                             0.4% 7.8% 0.0% 0.0%  1.1%                                                                              70.1%  8.9%                                                                              0.4% BG1                              26.0%                                                                             5.7% 1.5% 9.7% 0.7%  9.7%                                                                              46.7% 11.9%                                                                              15.4%                                                                              56A                              16.4%                                                                             1.4% 10.0%                                                                              1.9% 2.2% 46.4%                                                                              21.8% 58.6%                                                                              3.3% 11A-1                            23.7%                                                                             3.3% 10.5%                                                                              1.9% 1.8% 29.9%                                                                              28.9% 42.2%                                                                              5.2% 4A-1                             18.7%                                                                             6.9% 9.2% 11.9%                                                                              3.2% 25.2%                                                                              24.9% 37.5%                                                                              18.8%                                                                              17B                              15.4%                                                                             4.2% 7.3% 9.5% 0.9% 51.2%                                                                              11.6% 59.3%                                                                              13.7%                                                                              ATCC20891                        22.3%                                                                             3.9% 7.6% 23.5%                                                                              0.5% 22.1%                                                                              20.2% 30.2%                                                                              27.4%                                                                              S44                              14.4%                                                                             2.3% 15.0%                                                                              18.4%                                                                              0.7% 43.8%                                                                              5.5%  59.4%                                                                              20.7%                                                                              U30                              22.1%                                                                             7.8% 3.1% 12.7%                                                                              1.0% 14.9%                                                                              38.3% 19.0%                                                                              20.5%                                                                              59A                              18.1%                                                                             2.3% 6.9% 9.1% 0.8% 52.2%                                                                              10.6% 59.9%                                                                              11.4%                                                                              U37-2                            15.8%                                                                             3.9% 8.8% 11.6%                                                                              1.2% 53.3%                                                                              5.5%  63.3%                                                                              15.5%                                                                              S50W                             23.7%                                                                             3.8% 6.3% 6.9% 0.6% 43.0%                                                                              15.6% 50.0%                                                                              10.7%                                                                              ATCC20891                        10.0%                                                                             0.0% 0.0% 0.0% 0.0%  0.0%                                                                              90.0%  0.0%                                                                              0.0% UX                               16.6%                                                                             6.3% 11.9%                                                                              13.3%                                                                              1.7% 43.0%                                                                              7.3%  56.6%                                                                              19.5%                                                                              LW9                              17.3%                                                                             2.3% 8.4% 11.4%                                                                              0.7% 53.6%                                                                              6.5%  62.6%                                                                              13.6%                                                                              C32-2                            23.8%                                                                             1.2% 6.4% 2.5% 1.9% 34.4%                                                                              29.8% 42.6%                                                                              3.7% 5A-1                             17.1%                                                                             5.2% 11.1%                                                                              7.6% 2.2% 27.2%                                                                              29.6% 40.4%                                                                              12.9%                                                                              BG1                              25.4%                                                                             2.2% 9.6% 7.0% 1.1% 46.0%                                                                              8.8%  56.7%                                                                              9.1% U3                               16.9%                                                                             12.0%                                                                              6.6% 16.2%                                                                              0.4% 25.1%                                                                              22.8% 32.1%                                                                              28.2%                                                                              55B                              26.3%                                                                             2.6% 8.6% 2.0% 2.5% 32.4%                                                                              25.5% 43.5%                                                                              4.6% 18A                              19.4%                                                                             0.3% 9.8% 0.0% 0.3% 38.4%                                                                              31.7% 48.6%                                                                              0.3% 32B                              16.0%                                                                             16.7%                                                                              8.6% 18.4%                                                                              0.0% 22.5%                                                                              17.7% 31.1%                                                                              35.1%                                                                              56B                              18.6%                                                                             7.7% 11.4%                                                                              3.6% 4.3% 31.7%                                                                              22.7% 47.4%                                                                              11.2%                                                                              SX2                              17.8%                                                                             4.4% 16.2%                                                                              6.4% 3.7% 33.6%                                                                              17.8% 53.5%                                                                              10.9%                                                                              53B                              16.8%                                                                             2.7% 13.8%                                                                              20.5%                                                                              1.4% 39.3%                                                                              5.5%  54.4%                                                                              23.3%                                                                              S49                              20.8%                                                                             8.0% 8.9% 6.4% 1.7% 33.9%                                                                              20.3% 44.5%                                                                              14.4%                                                                              S3                               14.8%                                                                             0.3% 3.7% 3.9% 0.0% 69.9%                                                                              7.4%  73.6%                                                                              4.2% 3A-1                             28.1%                                                                             5.2% 12.7%                                                                              3.2% 0.9% 20.9%                                                                              29.0% 34.5%                                                                              8.4% 15A                              20.9%                                                                             0.7% 8.5% 1.0% 0.0% 35.8%                                                                              33.0% 44.3%                                                                              1.7% 9A-1                             15.7%                                                                             10.2%                                                                              8.8% 13.4%                                                                              1.5% 23.9%                                                                              26.3% 34.3%                                                                              23.7%                                                                              51B                              16.2%                                                                             11.2%                                                                              7.8% 16.4%                                                                              1.5% 20.4%                                                                              26.5% 29.7%                                                                              27.6%                                                                              8A-1                             20.5%                                                                             5.5% 8.6% 4.8% 2.7% 28.7%                                                                              29.2% 40.0%                                                                              10.3%                                                                              13A-1                            16.1%                                                                             13.6%                                                                              11.1%                                                                              16.0%                                                                              0.0% 28.4%                                                                              14.8% 39.4%                                                                              29.6%                                                                              24B-2                            16.9%                                                                             7.3% 16.4%                                                                              6.1% 0.0% 40.8%                                                                              12.4% 57.2%                                                                              13.4%                                                                              24B-1                            16.2%                                                                             0.0% 10.9%                                                                              1.0% 0.0% 56.5%                                                                              15.5% 67.4%                                                                              1.0% 3B                               17.0%                                                                             0.0% 5.0% 2.3% 0.0% 73.4%                                                                              2.3%  78.3%                                                                              2.3% SBG5                             20.8%                                                                             4.5% 5.8% 3.8% 1.0% 22.7%                                                                              41.3% 29.5%                                                                              8.4% 16B                              19.0%                                                                             14.0%                                                                              8.3% 18.9%                                                                              0.7% 23.9%                                                                              15.2% 32.9%                                                                              32.9%                                                                              6A-1                             18.0%                                                                             0.3% 10.1%                                                                              0.0% 0.0% 48.9%                                                                              22.7% 59.0%                                                                              0.3% 33B                              16.7%                                                                             5.5% 14.8%                                                                              8.5% 1.7% 31.8%                                                                              21.0% 48.3%                                                                              13.9%                                                                              B40                              15.0%                                                                             1.0% 11.7%                                                                              2.1% 0.9% 62.3%                                                                              6.9%  74.9%                                                                              3.1% 28A                              17.8%                                                                             18.5%                                                                              8.1% 20.5%                                                                              0.0% 22.1%                                                                              12.9% 30.2%                                                                              39.0%                                                                              43B                              16.9%                                                                             0.0% 3.4% 2.7% 0.0% 61.2%                                                                              15.8% 64.6%                                                                              2.7% 1A-1                             15.6%                                                                             2.7% 11.4%                                                                              10.9%                                                                              0.8% 53.7%                                                                              4.9%  65.9%                                                                              13.6%                                                                              U41-2                            16.5%                                                                             0.7% 3.9% 3.9% 0.0% 68.4%                                                                              6.7%  72.2%                                                                              4.6% 56B                              14.4%                                                                             0.9% 10.9%                                                                              2.5% 1.0% 66.4%                                                                              3.8%  78.3%                                                                              3.4% 46A                              17.6%                                                                             0.0% 2.4% 3.3% 0.0% 66.3%                                                                              10.4% 68.7%                                                                              3.3% 15A-1                            25.0%                                                                             0.0% 3.3% 0.0% 1.4% 53.2%                                                                              17.1% 57.9%                                                                              0.0% 13A                              16.1%                                                                             13.4%                                                                              9.3% 13.6%                                                                              0.0% 32.3%                                                                              15.3% 41.6%                                                                              27.0%                                                                              37B                              16.5%                                                                             9.1% 13.2%                                                                              6.7% 0.0% 38.9%                                                                              15.6% 52.1%                                                                              15.9%                                                                              43B                              16.1%                                                                             12.4%                                                                              12.0%                                                                              15.7%                                                                              0.8% 30.5%                                                                              12.5% 43.3%                                                                              28.1%                                                                              17B                              13.8%                                                                             0.8% 11.5%                                                                              2.8% 0.0% 67.0%                                                                              4.1%  78.6%                                                                              3.6% 27A                              17.5%                                                                             18.6%                                                                              9.0% 19.5%                                                                              0.0% 21.7%                                                                              13.7% 30.7%                                                                              38.1%                                                                              46B                              21.4%                                                                             1.4% 18.9%                                                                              0.0% 5.0% 43.5%                                                                              9.9%  67.3%                                                                              1.4% ATCC20890                        17.7%                                                                             0.0% 0.6% 4.4% 0.0% 68.2%                                                                              9.1%  68.8%                                                                              4.4% 5A                               17.6%                                                                             16.0%                                                                              9.6% 18.8%                                                                              0.0% 25.6%                                                                              12.4% 35.2%                                                                              34.8%                                                                              28B-2                            14.0%                                                                             0.9% 13.2%                                                                              1.6% 0.0% 64.7%                                                                              5.5%  77.9%                                                                              2.6% 27B                              19.5%                                                                             2.9% 16.6%                                                                              1.1% 1.6% 30.2%                                                                              28.1% 48.5%                                                                              4.0% 49B                              17.2%                                                                             0.7% 6.8% 2.7% 0.0% 63.0%                                                                              9.6%  69.8%                                                                              3.4% 18B                              14.4%                                                                             3.5% 13.5%                                                                              26.0%                                                                              1.0% 37.2%                                                                              4.4%  51.6%                                                                              29.5%                                                                              S49-2                            16.1%                                                                             2.2% 15.7%                                                                              21.6%                                                                              0.0% 36.7%                                                                              7.8%  52.4%                                                                              23.7%                                                                              20B                              17.3%                                                                             4.7% 14.3%                                                                              7.2% 2.9% 30.2%                                                                              23.5% 47.3%                                                                              11.9%                                                                              8B                               11.5%                                                                             3.3% 11.3%                                                                              6.5% 1.1% 59.9%                                                                              6.5%  72.2%                                                                              9.8% 13B                              16.6%                                                                             0.7% 10.7%                                                                              1.6% 0.0% 59.7%                                                                              10.8% 70.4%                                                                              2.2% 26A                              16.1%                                                                             3.3% 13.5%                                                                              23.8%                                                                              0.0% 38.7%                                                                              4.7%  52.2%                                                                              27.1%                                                                              S42                              15.6%                                                                             0.6% 12.1%                                                                              0.0% 0.0% 60.2%                                                                              11.5% 72.3%                                                                              0.6% 35B                              19.5%                                                                             0.0% 1.4% 3.4% 0.0% 66.6%                                                                              9.1%  68.0%                                                                              3.4% 42A                              18.9%                                                                             3.5% 12.7%                                                                              25.0%                                                                              0.0% 35.0%                                                                              5.0%  47.6%                                                                              28.5%                                                                              40A                              25.2%                                                                             3.3% 9.3% 21.8%                                                                              0.0% 30.3%                                                                              10.1% 39.6%                                                                              25.1%                                                                              S50C                             17.6%                                                                             11.1%                                                                              13.2%                                                                              14.1%                                                                              1.3% 28.7%                                                                              14.0% 43.2%                                                                              25.2%                                                                              59A                              19.9%                                                                             0.0% 5.5% 1.9% 0.0% 66.8%                                                                              6.0%  72.3%                                                                              1.9% SBG9                             15.4%                                                                             3.1% 13.2%                                                                              26.1%                                                                              0.0% 35.8%                                                                              6.5%  49.1%                                                                              29.1%                                                                              21B                              18.9%                                                                             0.7% 11.6%                                                                              0.0% 0.0% 59.1%                                                                              9.7%  70.7%                                                                              0.7% 2B                               14.1%                                                                             1.1% 12.4%                                                                              2.0% 0.0% 65.2%                                                                              5.2%  77.6%                                                                              3.1% 1B                               22.2%                                                                             16.2%                                                                              6.3% 17.7%                                                                              0.0% 18.1%                                                                              19.5% 24.4%                                                                              33.8%                                                                              55B                              16.0%                                                                             1.0% 4.5% 0.0% 0.0% 69.5%                                                                              9.0%  74.0%                                                                              1.0% 3A                               17.0%                                                                             4.3% 12.4%                                                                              29.8%                                                                              0.0% 34.0%                                                                              2.5%  46.4%                                                                              34.1%                                                                              9B                               15.4%                                                                             4.3% 8.7% 13.2%                                                                              0.0% 53.2%                                                                              5.1%  62.0%                                                                              17.5%                                                                              U24                              14.2%                                                                             3.1% 12.0%                                                                              20.0%                                                                              1.1% 35.2%                                                                              14.3% 48.3%                                                                              23.2%                                                                              U28                              16.8%                                                                             14.6%                                                                              10.1%                                                                              16.0%                                                                              0.6% 27.7%                                                                              14.0% 38.5%                                                                              30.7%                                                                              28B-1                            23.2%                                                                             1.9% 8.3% 1.1% 2.3% 22.7%                                                                              40.4% 33.3%                                                                              3.0% 44B                              24.6%                                                                             15.8%                                                                              8.7% 16.0%                                                                              0.0% 15.3%                                                                              19.6% 24.0%                                                                              31.8%                                                                              54B                              15.5%                                                                             0.0% 1.3% 2.9% 0.0% 72.7%                                                                              7.6%  74.0%                                                                              2.9% 55A                              18.4%                                                                             1.0% 5.0% 3.0% 0.0% 66.2%                                                                              6.4%  71.3%                                                                              3.9% 49A                              18.6%                                                                             15.3%                                                                              9.4% 18.0%                                                                              0.0% 27.3%                                                                              11.4% 36.7%                                                                              33.3%                                                                              51A                              23.5%                                                                             13.1%                                                                              7.3% 17.9%                                                                              0.0% 26.7%                                                                              11.4% 34.0%                                                                              31.0%                                                                              14A-1                            13.3%                                                                             1.1% 14.5%                                                                              0.9% 0.0% 64.6%                                                                              5.6%  79.1%                                                                              2.0% 25B                              22.9%                                                                             2.4% 10.3%                                                                              21.5%                                                                              0.0% 26.5%                                                                              16.4% 36.9%                                                                              23.9%                                                                              41A                              16.8%                                                                             1.0% 9.7% 2.7% 0.0% 58.3%                                                                              11.5% 68.0%                                                                              3.7% 24A                               0.4%                                                                             8.5% 14.1%                                                                              10.2%                                                                              2.1% 27.6%                                                                              37.0% 43.8%                                                                              18.8%                                                                              61A                              30.5%                                                                             0.0% 7.1% 0.0% 0.0%  0.6%                                                                              61.8%  7.7%                                                                              0.0% BRBG                             18.2%                                                                             14.9%                                                                              8.3% 18.7%                                                                              0.0% 24.4%                                                                              15.5% 32.7%                                                                              33.6%                                                                              17A                              17.4%                                                                             2.0% 9.3% 2.8% 0.0% 55.7%                                                                              12.7% 65.0%                                                                              4.9% 60A                              14.1%                                                                             0.8% 13.0%                                                                              1.2% 0.0% 67.8%                                                                              3.1%  80.8%                                                                              2.0% 26B                              17.8%                                                                             5.0% 6.9% 15.0%                                                                              1.5% 47.4%                                                                              6.4%  55.8%                                                                              20.0%                                                                              ATCC20888                        16.0%                                                                             0.0% 1.8% 2.0% 0.0% 70.8%                                                                              9.4%  72.6%                                                                              2.0% 2A                               24.6%                                                                             0.0% 4.0% 0.0% 0.0% 49.4%                                                                              22.0% 53.4%                                                                              0.0% 44A                              17.4%                                                                             1.8% 0.0% 2.9% 0.0% 55.3%                                                                              23.3% 55.3%                                                                              4.6% 14A                              23.3%                                                                             1.3% 4.6% 0.0% 0.0% 12.6%                                                                              58.1% 17.3%                                                                              1.3% 41B                              19.3%                                                                             0.0% 1.1% 3.8% 0.0% 66.6%                                                                              9.1%  67.8%                                                                              3.8% 66A                              18.6%                                                                             15.6%                                                                              8.3% 17.1%                                                                              1.1% 24.6%                                                                              14.8% 33.9%                                                                              32.7%                                                                              11A                              19.6%                                                                             5.1% 10.1%                                                                              27.2%                                                                              0.0% 27.5%                                                                              10.6% 37.5%                                                                              32.3%                                                                              2X                               15.7%                                                                             2.4% 14.0%                                                                              25.7%                                                                              0.0% 36.7%                                                                              5.4%  50.8%                                                                              28.1%                                                                              33A                              14.6%                                                                             1.5% 13.5%                                                                              0.0% 0.0% 66.0%                                                                              4.3%  79.5%                                                                              1.5% ATCC20892                        PRIOR STRAINS                                                                 15.7%                                                                             3.9% 3.7% 8.1% 0.0% 55.1%                                                                              13.5% 58.8%                                                                              12.0%                                                                              ATCC34304                        28.2%                                                                             1.6% 6.9% 11.4%                                                                              0.0% 17.8%                                                                              34.1% 24.7%                                                                              12.9%                                                                              ATCC24473                        15.2%                                                                             2.9% 7.7% 9.8% 0.6% 54.6%                                                                              9.2%  62.9%                                                                              12.7%                                                                              ATCC28211                        23.2%                                                                             10.7%                                                                              4.3% 12.6%                                                                              1.5% 20.6%                                                                              27.0% 26.4%                                                                              23.4%                                                                              ATCC28209                        13.2%                                                                             6.3% 6.9% 4.3% 0.0% 60.1%                                                                              9.1%  67.0%                                                                              10.6%                                                                              ATCC28210                        __________________________________________________________________________

                  TABLE 4                                                         ______________________________________                                        EPA       DPA      DHA                                                        C20:5w3   C22:5w3  C22:6w3      Strain                                        ______________________________________                                        COMPOSITION OF OMEGA 3                                                        FATTY ACID FRACTION                                                           44.0%     1.1%     54.9%        21                                             4.6%     0.9%     94.5%        ATCC20889                                     19.3%     0.7%     80.0%        U40-2                                         31.9%     0.0%     68.1%        21B                                           87.9%     0.0%     12.1%        BRBG1                                         12.5%     6.1%     81.5%        56A                                           17.0%     3.7%     79.3%        11A-1                                         24.9%     4.3%     70.8%        4A-1                                          24.4%     8.4%     67.2%        17B                                           12.2%     1.5%     86.3%        ATCC20891                                     25.1%     1.7%     73.2%        S44                                           25.2%     1.1%     73.7%        U30                                           16.2%     5.4%     78.4%        59A                                           11.5%     1.4%     87.1%        U37-2                                         14.0%     1.9%     84.2%        S50W                                          12.7%     1.3%     86.0%        ATCC20891                                     --        --       --           UX                                            21.0%     2.9%     76.1%        LWN9                                          13.4%     1.0%     85.6%        C32-2                                         15.0%     4.3%     80.7%        5A-1                                          27.4%     5.4%     67.2%        BRBG1                                         17.0%     1.9%     81.1%        U3                                            20.5%     1.3%     78.2%        55B                                           19.8%     5.8%     74.4%        18A                                           20.1%     0.7%     79.2%        32B                                           27.8%     0.0%     72.2%        56B                                           24.1%     9.1%     66.9%        SX2                                           30.3%     6.9%     62.8%        53B                                           25.3%     2.5%     72.2%        S49                                           19.9%     3.8%     76.3%        S3                                             5.0%     0.0%     95.0%        3A-1                                          36.9%     2.6%     60.5%        15A                                           19.3%     0.0%     80.7%        9A-1                                          25.8%     4.4%     69.8%        51B                                           26.3%     5.0%     68.7%        8A-1                                          21.6%     6.7%     71.7%        13A-1                                         28.0%     0.0%     72.0%        24B-2                                         28.7%     0.0%     71.3%        24B-1                                         16.2%     0.0%     83.8%        3B                                             6.3%     0.0%     93.7%        SBG5                                          19.7%     3.3%     77.0%        16B                                           25.2%     2.1%     72.6%        6A-1                                          17.1%     0.0%     82.9%        33B                                           30.5%     3.6%     65.9%        B40                                           15.6%     1.2%     83.1%        28A                                           26.8%     0.0%     73.2%        43B                                            5.2%     0.0%     94.8%        1A-1                                          17.4%     1.2%     81.5%        U41-2                                          5.4%     0.0%     94.6%        56B                                           13.9%     1.3%     84.8%        46A                                            3.5%     0.0%     96.5%        15A-1                                          5.8%     2.4%     91.8%        13A                                           22.3%     0.0%     77.7%        37B                                           25.4%     0.0%     74.6%        43B                                           27.7%     1.9%     70.3%        17B                                           14.7%     0.0%     85.3%        27A                                           29.2%     0.0%     70.8%        46B                                           28.0%     7.5%     64.5%        ATCC20890                                      0.9%     0.0%     99.1%        5A                                            27.3%     0.0%     72.7%        28B-2                                         16.9%     0.0%     83.1%        27B                                           34.3%     3.4%     62.3%        49B                                            9.7%     0.0%     90.3%        18B                                           26.1%     1.9%     71.9%        S49-2                                         29.9%     0.0%     70.1%        20B                                           30.1%     6.2%     63.7%        8B                                            15.6%     1.5%     82.9%        13B                                           15.2%     0.0%     84.8%        26A                                           25.9%     0.0%     74.1%        S42                                           16.7%     0.0%     83.3%        35B                                            2.1%     0.0%     97.9%        42A                                           26.6%     0.0%     73.4%        40A                                           23.4%     0.0%     76.6%        S50C                                          30.6%     2.9%     66.4%        59A                                            7.6%     0.0%     92.4%        SBG9                                          27.0%     0.0%     73.0%        21B                                           16.4%     0.0%     83.6%        2B                                            15.9%     0.0%     84.1%        1B                                            25.9%     0.0%     74.1%        55B                                            6.0%     0.0%     94.0%        3A                                            26.7%     0.0%     73.3%        9B                                            14.1%     0.0%     85.9%        U24                                           24.9%     2.2%     72.9%        U28                                           26.4%     1.5%     72.1%        28B-1                                         24.8%     6.9%     68.3%        44B                                           36.4%     0.0%     63.6%        54B                                            1.8%     0.0%     98.2%        55A                                            7.1%     0.0%     92.9%        49A                                           25.6%     0.0%     74.4%        51A                                           21.5%     0.0%     78.5%        14A-1                                         18.4%     0.0%     81.6%        25B                                           28.1%     0.0%     71.9%        41A                                           14.3%     0.0%     85.7%        24A                                           32.3%     4.8%     63.0%        61A                                           91.6%     0.0%     8.4%         BRBG                                          25.5%     0.0%     74.5%        17A                                           14.4%     0.0%     85.6%        60A                                           16.1%     0.0%     83.9%        26B                                           12.4%     2.7%     84.9%        ATCC20888                                      2.5%     0.0%     97.5%        2A                                             7.5%     0.0%     92.5%        44A                                            0.0%     0.0%     100.0%       14A                                           26.7%     0.0%     73.3%        41B                                            1.7%     0.0%     98.3%        66A                                           24.5%     3.1%     72.4%        11A                                           26.8%     0.0%     73.2%        2X                                            27.6%     0.0%     72.4%        33A                                           17.0%     0.0%     83.0%        ATCC20892                                     PRIOR STRAINS                                                                  6.4%     0.0%     93.6%        ATCC34304                                     27.9%     0.0%     72.1%        ATCC24473                                     12.2%     1.0%     86.8%        ATCC28211                                     16.4%     5.6%     78.1%        ATCC28209                                     10.3%     0.0%     89.7%        ATCC28210                                     ______________________________________                                    

Example 6. Enhanced growth rates of strains isolated by method inExample 1 compared to ATCC strains (previously known strains

Cells of Schizochytrium sp. S31 (ATCC No. 20888), Schizochytrium sp. S8(ATCC No. 20889), Thraustochytrium sp. S42, Thraustochytrium sp. U42-2,Thraustochytrium sp. S42 and U30, (all isolated by the method ofExample 1) and Thraustochytrium aureum (ATCC #28211) and Schizochytriumaggregatum (ATCC #28209) (previously known strains) were picked fromsolid F-1 medium and placed into 50 ml of M-5 medium. This mediumconsists of (on a per liter basis): Yeast Extract, 1 g; NaCl, 25 g;MgSO₄.7H₂ O, 5 g; KCl, 1 g; CaCl₂, 200 mg; glucose, 5 g; glutamate, 5 g;KH₂ PO₄, 1 g; PII metals, 5 ml; A-vitamins solution, 1 ml; andantibiotic solution, 1 ml. The pH of the solution was adjusted to 7.0and the solution was filter sterilized. After three days of growth on anorbital shaker (200 rpm, 27° C.), 1-2 ml of each culture was transferredto another flask of M-5 medium and placed on the shaker for 2 days. Thecultures (1-2 ml) were then transferred to another flask of M-5 mediumand placed on the shaker for 1 day. This process ensured that allcultures were in the exponential phase of growth. These later cultureswere then used to inoculate two 250 ml flasks of M-5 medium for eachstrain. These flasks were than placed on shakers at 25° C. and 30° C.,and changes in their optical density were monitored on a Beckman DB-Gspectrophotometer (660nm, 1 cm path length). Optical density readingswere taken at the following times: 0, 6, 10, 14, 17.25, 20.25 and 22.75hours. Exponential growth rates (doublings/day) were then calculatedfrom the optical density data by the method of Sorokin (1973). Theresults are presented in Table 5 and illustrated (normalized to thegrowth of strain U30 at 25° C.) in FIG. 5. The data indicate that thestrains isolated by the method in Example 1 have much higher growthrates than the previously known ATCC strains at both 25° C. and 30° C.,even under the optimized phosphate levels essential for continuousgrowth. Strains of Thraustochytriales isolated from cold Antarcticwaters have not been shown to grow at 30° C.

                  TABLE 5                                                         ______________________________________                                        Exponential Growth Rate                                                       (doublings/day)                                                               Strain          25° C.                                                                         30° C.                                         ______________________________________                                        S31*            8.5     9.4                                                   U40-2*          5.8     6.0                                                   S8*             7.1     8.8                                                   S42*            6.6     8.3                                                   U30*            5.5     7.3                                                   28209**         4.6     5.0                                                   28210**         3.5     4.5                                                   28211**         4.2     5.7                                                   34304**         2.7     3.7                                                   24473**         4.6     5.3                                                   ______________________________________                                         *strain isolated by method in Example 1                                       **previously known ATCC strain                                           

Example 7. Enhanced production characteristics (growth and lipidinduction) of strains isolated by method in Example 1 compared to ATCCstrains (prior art strains)

Cells of Schizochytrium sp. S31 (ATCC No. 20888), Schizochytrium sp. S8(ATCC No. 20889) (both isolated by the method of Example 1) andThraustochytrium aureum (ATCC #28211) and Schizochytrium aggregatum(ATCC #28209) (prior art strains) were picked from solid F-1 medium andplaced into 50 ml of M-5 medium (see Example 5) The pH of the solutionwas adjusted to 7.0 and the solution was filter sterilized. After threedays of growth on an orbital shaker (200 rpm, 27° C.), 1-2 ml of eachculture was transferred to another flask of M-5 medium and placed on theshaker for 2 days. The ash-free dry weights for each of these cultureswere then quickly determined and 3.29 mg of each culture was pipettedinto two 250 ml erlenmeyer flasks containing 50 ml of M-5 medium. Theseflasks were placed on a rotary shaker (200 rpm, 27° C.). After 24 hours20 ml portions of each culture were then centrifuged, the supernatantsdiscarded, and the cells transferred to 250 ml erlenmeyer flaskscontaining 50 ml of M-5 medium without any glutamate (N-source). Theflasks were placed back on the shaker, and after another 12 hours theywere sampled to determine ash-free dry weights and quantify fatty acidcontents by the method of Lepage and Roy (1984). The results areillustrated (normalized to the yields of ATCC No. 28211, previouslyknown strain) in FIG. 6. The results indicate that the strains isolatedby the method of Example 1 produced 2-3 times as much ash-free dryweight in the same period of time, under a combination of exponentialgrowth and nitrogen limitation (for lipid induction) as the prior artATCC strains. In addition, higher yields of total fatty acids andomega-3 fatty acids were obtained from strains of the present inventionwith strains S31 (ATCC No. 20888) producing 3-4 times as much omega-3fatty acids as the prior art ATCC strains.

Example 8. Enhanced salinity tolerance and fatty acid production bystrains isolated by method in Example 1

Strains of 4 species of Thraustochytrids, Schizochytrium sp. S31 (ATCCNo. 20888) and Thraustochytrium sp. U42-2 (ATCC No. 20891) (bothisolated and screened by the method of Example 1), and S. aggregatum(ATCC 28209) and T. aureum (ATCC 28210) (obtained from the American TypeCulture Collection) were picked from solid F-1 medium and incubated for3-4 days at 27° C. on a rotary shaker (200 rpm). A range of differingsalinity medium was prepared by making the following dilutions of Mmedium salts (NaCl, 25 g/1; MgSO₄.7H₂ O, 5 g/1; KCl, 1 g/1; CaCl₂, 200mg/1: 1) 100% (w/v M medium salts; 2) 80% (v/v) M medium, 20% (v/v)distilled water; 3) 60% (v/v) M medium, 40% (v/v) distilled water; 4)40% (v/v) M medium, 60% (v/v) distilled water; 5) 20% (v/v) M medium,80% distilled water; 6) 15% (v/v) M medium, 85% (v/v) distilled water;7) 10% (v/v) M medium, 90% (v/v) distilled water; 8) 7% (v/v) M medium,93% (v/v) distilled water; 9) 3% (v/v) M medium, 97% (v/v) distilledwater; 10) 1.5% (v/v) M medium, 98.5% (v/v) distilled water. Thefollowing nutrients were added to the treatments (per liter): glucose, 5g; glutamate, 5 g; yeast ext., 1 g; (NH4)2S04, 200 mg; NaHC03, 200 mg;KH₂ PO₄,1 g/l; PII metals, 5 ml; A-vitamins solution,1 ml; andantibiotics solution, 2 ml. Fifty ml of each of these treatments wereinoculated with1 ml of the cells growing in the F-1 medium. Thesecultures were placed on an orbital shaker (200 rpm) and maintained at27° C. for 48 hr. The cells were harvested by centrifugation and totalfatty acids determined by gas chromatography. The results areillustrated in FIG. 7. Thraustochytrium sp. U42-2 (ATCC No. 20891)isolated by the method of Example 1 can yield almost twice the amount offatty acids produced by T. aureum (ATCC 28210) and over 8 times theamount of fatty acids produced by S. aggregatum (ATCC 28209).Additionally, U42-2 appears to have a wider salinity tolerance at theupper end of the salinity range evaluated. Schizochytrium sp. S31 (ATCCNo. 20888), also isolated by the method in Example 1, exhibited both ahigh fatty acid yield (2.5 to 10 times that of the previously known ATCCstrains) and a much wider range of salinity tolerance than the ATCCstrains. Additionally, Schizochytrium sp. S31 (ATCC No. 20888) growsbest at very low salinities. This property provides a strong economicadvantage when considering commercial production, both because of thecorrosive effects of saline waters on metal reactors, and because ofproblems associated with the disposal of saline waters.

Example 9. Cultivation/Low Salinity

Fifty ml of M/10-5 culture media in a 250 ml erlenmeyer flask wasinoculated with a colony of Schizochytrium sp. S31 (ATCC No. 20888)picked from an agar slant. The M/10-5 media contains: 1000 ml deionizedwater, 2.5 g NaCl, 0.5 g MgSO₄ 7H₂ O, 0.1 g KCl, 0.02 g CaCl₂, 1.0 g KH₂PO₄, 1.0 g yeast extract, 5.0 g glucose, 5.0 g glutamic acids, 0.2 gNaHC03, 5 ml PII trace metals, 2 ml vitamin mix, and 2 ml antibioticmix. The culture was incubated at 30° C. on a rotary shaker (200 rpm).After 2 days the culture was at a moderate density and actively growing.20 ml of this actively growing culture was used to inoculate a 2 literfermenter containing 1700 ml of the same culture media except theconcentration of the glucose and glutamate had been increased to 40 g/1(M/10-40 media). The fermenter was maintained at 30° C., with aerationat 1 vol/vol/min, and mixing at 300 rpm. After 48 hr, the concentrationof cells in the fermenter was 21.7 g/l. The cells were harvested bycentrifugation, lyophilized, and stored under N₂.

The total fatty acid content and omega-3 fatty acid content wasdetermined by gas chromatography. The total fatty acid content of thefinal product was 39.0% ash-free dry weight. The omega-3 highlyunsaturated fatty acid content (C20:5w3, C22:5w3 and C22:6w3) of themicrobial product was 25.6% of the ash-free dry weight. The ash contentof the sample was 7.0%.

Example 10

Growth and gas chromatographic analysis of fatty acid production byvarious strains as described in example 5 revealed differences in fattyacid diversity. Strains of the present invention synthesized fewerdifferent fatty acids than previously available strains. Lower diversityof fatty acids is advantageous in fatty acid purification since thereare fewer impurities to be separated. For food supplement purposes,fewer different fatty acids is advantageous because the likelihood ofingesting unwanted fatty acids is reduced. Table 6 shows the number ofdifferent highly unsaturated fatty acids present, at concentrationsgreater than 1% by weight of total fatty acids for previously knownstrains, designated by ATCC number and various strains of the presentinvention.

                  TABLE 6                                                         ______________________________________                                                    No. of Different Fatty                                                        Acids at 1% or Greater                                            Strain      % of Total Fatty Acids                                            ______________________________________                                        34304**     8                                                                 28211**     8                                                                 24473**     10                                                                28209**     13                                                                28210**     8                                                                 S31*        5                                                                 S8*         6                                                                 79B*        6                                                                 ______________________________________                                         *strain isolated by the method in Example 1                                   **previously known ATCC strain                                           

Example 11. Recovery

Fifty ml of M5 culture media in a 250 ml erlenmeyer flask was inoculatedwith a colony of Schizochytrium sp. S31 (ATCC No. 20888) picked from anagar slant. The M5 media contains: 1000 ml deionized water, 25.0 g NaCl,5.0 g MgSO4.7H₂ O, 1.0 g KCl, 0.2 g CaCl₂, 1.0 g KH₂ PO₄, 1.0 g yeastextract, 5.0 g glucose, 5.0 g glutamic acid, 0.2 g NaHCO₃,5 ml PII tracemetals, 2 ml vitamin mix, and 2 ml antibiotic mix. The culture wasincubated at 30° C. on a rotary shaker (200 rpm). After 2 days theculture was at a moderate density and actively growing. 20 ml of thisactively growing culture was used to inoculate an 1 liter fermentercontaining 1000 ml of the same culture media except the concentration ofthe glucose and glutamate had been increased to 40 g/l (M20 media). Thefermenter was maintain at 30° C. and pH 7.4, with aeration at 1 vol/min,and mixing at 400 rpm. After 48 hr, the concentration of the cells inthe fermenter was 18.5 g/l. Aeration and mixing in the fermenter wasturned off. Within 2-4 minutes, the cells flocculated and settled in thebottom 250 ml of the fermenter. This concentrated zone of cells had acell concentration of 72 g/l. This zone of cells can be siphoned fromthe fermenter, and: (1) transferred to another reactor for a period ofnitrogen limitation (e.g., combining the highly concentrated productionof several fermenters); or (2) harvested directly by centrifugation orfiltration. By preconcentrating the cells in this manner, 60-80% lesswater has to be processed to recover the cells.

Example 12. Utilization of a variety of carbon and nitrogen sources

Fifty ml of M5 culture media in a 250 ml erlenmeyer flask was inoculatedwith a colony of Schizochytrium sp. S31 (ATCC No. 20888) orThraustochytrium sp. U42-2 (ATCC No. 20891) picked from an agar slant.The M5 media was described in Example 4 except for 2 ml vitamin mix, and2 ml antibiotic mix. The culture was incubated at 30° C. on a rotaryshaker (200 rpm). After 2 days the culture was at a moderate density andactively growing. This culture was used to inoculate flasks of M5 mediawith one of the following substituted for the glucose (at 5 g/l):dextrin, sorbitol, fructose, lactose, maltose, sucrose, corn starch,wheat starch, potato starch, ground corn; or one of the followingsubstituted for the glutamate (at 5 g/l): gelysate, peptone, tryptone,casein, corn steep liquor, urea, nitrate, ammonium, whey, or corn glutenmeal. The cultures were incubated for 48 hours on a rotary shaker (200rpm, 27° C.). The relative culture densities, representing growth on thedifferent organic substrates, are illustrated in Tables 7-8.

                  TABLE 7                                                         ______________________________________                                        Utilization of Nitrogen Sources                                                        Strains                                                                          Thraustochytrium                                                                           Schizochytrium                                                  sp. U42-2    sp. S31                                               N-Source   ATCC No. 20891                                                                             ATCC No. 20888                                        ______________________________________                                        glutamate  +++          +++                                                   gelysate   +++          +++                                                   peptone     ++           ++                                                   tryptone    ++           ++                                                   casein      ++           ++                                                   corn steep +++          +++                                                   liquor                                                                        urea         +           ++                                                   nitrate     ++          +++                                                   ammonium     +          +++                                                   whey       +++          +++                                                   corn gluten                                                                              +++          +++                                                   meal                                                                          ______________________________________                                         +++ = high growth                                                             ++ = medium growth                                                            + = low growth                                                                0 = no growth                                                            

                  TABLE 8                                                         ______________________________________                                        Utilization of Organic Carbon Sources.                                                 Strains                                                                          Thraustochytrium                                                                           Schizochytrium                                                  sp. U42-2    sp. S31                                               C-Source   ATCC No. 20891                                                                             ATCC No. 20888                                        ______________________________________                                        glucose    +++          +++                                                   dextrin    +++          +++                                                   sorbitol     +            +                                                   fructose     +          +++                                                   lactose      +            +                                                   maltose    +++            +                                                   sucrose      +            +                                                   corn starch                                                                              +++            +                                                   wheat starch                                                                             +++            +                                                   potato starch                                                                            +++            +                                                   ground corn                                                                              +++             0                                                  ______________________________________                                         +++ = high growth                                                             ++ = medium growth                                                            + = low growth                                                                0 = no growth                                                            

Example 13. Feeding of thraustochytrid-based feed supplement to brineshrimp to increase their omega-3 HUFA content

Cellular biomass of Thraustochytrium sp. 12B (ATCC 20890) was producedin shake flasks in M-5 medium (see Example 6) at 25° C. Cellular biomassof Thraustochytrium sp. S31 (ATCC 20888) was produced in shake flasks inM-5/10 medium (see Example 9) at 27° C. The cells of each strain wereharvested by centrifugation. The pellet was washed once with distilledwater and recentrifuged to produce a 50% solids paste. The resultingpaste was resuspended in sea water and then added to an adult brineshrimp culture as a feed supplement. The brine shrimp had previouslybeen reared on agricultural waste products and as a result their omega-3HUFA content was very low, only 1.3-2.3% of total fatty acids(wild-caught brine shrimp have an average omega-3 HUFA content of 6-8%total fatty acids). The brine shrimp (2-3/mL) were held in a 1 literbeaker filled with sea water and an airstone was utilized to aerate andmix the culture. After addition of the feed supplement, samples of thebrine shrimp were periodically harvested, washed, and their fatty acidcontent determined by gas chromatography. The results are illustrated inFIGS. 8 -9. When fed the thraustochytrid-based feed supplement as afinishing feed, the omega-3 content of the brine shrimp can be raised tothat of wild-type brine shrimp within 5 hours if fed strain 12B orwithin 11 hours when fed strain S31. The omega-3 HUFA content of thebrine shrimp can be greatly enhanced over that of the wild type if fedthese feed supplements for up to 24 hours. Additionally, these feedsupplements greatly increase the DHA content of the brine shrimp, whichis generally only reported in trace levels in wild-caught brine shrimp.

Example 14. Feeding of thraustochytrid-based feed supplement to layinghens to produce omega-3 HUFA enriched eggs

Cellular biomass of Thraustochytrium sp. S31 (ATCC 20888) was producedin a 10 liter fermenter in M-5/10 medium (see Example 9) at 27° C. Thecells of Thraustochytrium sp. S31 (ATCC 20888) were harvested bycentrifugation, washed once with distilled water and recentrifuged toproduce a 50% solids paste. This cell paste was then treated in one oftwo ways: lyophilized; or 2) mixed with ground corn to produce a 70%solids paste and then extruded at 90°-120° C. and air dried. Theresulting dried products were then ground, analyzed for omega-3 HUFAcontent, and mixed into layers rations at a level to provide 400 mg ofomega-3 HUFA per day to the laying hens (400 mg omega-3 HUFA/100 gramslayers ration). The resulting eggs were sampled over a period ofapproximately 45 days and analyzed by gas chromatography for omega-3HUFA's. Eggs with up to 200 -425 mg omega-3 HUFA's/egg were produced bythe hen fed omega-3 supplement. When cooked, these eggs did not exhibitany fishy odors. The control hens produced eggs with only approximately20 mg omega-3 HUFA/egg. There was no significant difference between thenumber of eggs laid by the control group and the hen fed the omega-3supplement. There was also no difference in the color of yolks of theeggs produced with the feed supplement and the control diet.

Example 15. Production of high purity (>90% purity omega-3 HUFA or >90%purity HUFA fatty acids mixtures)

Cellular biomass of Thraustochytrium sp. S31 (ATCC 20888) was producedin a 10 liter fermenter in M-5/10 medium (see Example 9) at 27° C. Thecells of this strain were harvested by centrifugation. Approximately 5 gof the cell paste was placed in the 350 mL stainless steel grindingchamber of a Bead-Beater bead mill which was filled 1/2 way with 0.5 mmglass beads. The remaining volumes of the chamber was filled withreagent grade MeOH and the cells homogenized for two 3 minute periods.During the bead mill operation, the stainless steel chamber was keptcold by an attached ice bath. The solution of broken cells was pouredinto a flask to which was added both chloroform and a 2 M NaCl solutionin water to bring the final solution to approximately 1:1:0.9(chloroform:MeOH:water). The solution was then poured into a separatoryfunnel and shaken several times to help move the lipids into thechloroform fraction. After the solution was allowed to settle forseveral minutes, the chloroform fraction was collected into a flask,another portion of fresh chloroform added to the separatory funnel andthe extraction repeated. This fraction of chloroform was then collectedfrom the separatory funnel and the two chloroform portions combined. Thechloroform was then removed (and recovered) by using a roto-vap rotaryvacuum evaporation device operated at 40° C. A portion (300 mg) of theremaining lipids was removed and hydrolyzed for 6 hours at 60° C. (undernitrogen gas) in 50 mL of solution of methanolic NaOH (10 mL of 0.3 NNaOH diluted to 100 mL with MeOH) in a 150 mL teflon lined screw cappedbottle. The nonsaponifiable materials (sterols, hydrocarbons, etc.) werethen removed by phase separating the solution with two 50 mL portions ofpetroleum either in a separatory funnel, discarding the ether fractioneach time. The remaining solution was then acidified by addition of 3 mLof 6 N HCl and the free fatty acids extracted with two 50 mL portions ofpetroleum ether. Five mL portion of the ether solution containing thefree fatty acids was placed in three 13 mm×100 mm test tubes and theether removed by blowing down the solution under a flow of nitrogen gas.Two mL portions of either petroleum ether, hexane or acetone were thenadded to one of tubes, which was then caped and placed in a solution ofdry ice and ethanol (-72° to -74° C.) to allow the non-HUFA fatty acidsto crystallize. When crystallization appeared complete, the culturetubes were placed in 50 mL polycarbonate centrifuge tubes that had beenfilled with finely powdered dry ice. These tubes were then placed in arefrigerated centrifuge at -10° C. and centrifuged for 3-5 minutes to10,000 rpm. The supernatant was then quickly removed from each tube witha pasteur pipet and placed in a clean culture tube. The solvent wasremoved from the supernatants by blowing down under N₂. The fatty acidswere then methylated in methanolic H₂ SO₄ (4 mL H₂ SO₄ in 96 mL MeoH) at100° C. for 1 hr. in teflon lined, screw capped tubes under N₂. Thefatty acid methyl esters were then quantified by gas chromatography (HP5890 gas chromatograph, Supelco SP 2330 column; column tepm=200° C.;detector and injector temp=250° C.; carrier gas=nitrogen). Thecomposition of the fatty acid mixtures obtained were: (ether) 93.1%HUFA's-23.4% C22:5n- 6+69.7% 22.6n-3:(hexane) 91.5% HUFA's-66.8%22.6n-3+22.1% 22:5n-6°2.6% 20:5n-3; (acetone) 90.0% HUFA's-65.6%22:6n-3+21.8n-6+2.6% 20:5n-3.

A fatty acid mixture containing >90% omega-3 UFA's can be obtained byrunning the above process on harvested biomass of the strain ofthraustochytrid such as 12B (ATCC 20890).

General Concluding Remarks

The following novel strains, isolated according to the method of theinvention, were placed on deposit at the American Type CultureCollection (ATCC), Rockville, Md, as exemplars of the organismsdisclosed and claimed herein.

    ______________________________________                                        Strain           ATCC No.  Deposit Date                                       ______________________________________                                         Schizochytrium S31                                                                            20888     8/8/88                                             Schizochytrium S8                                                                              20889     8/8/88                                             Schizochytrium 12B                                                                             20890     8/8/88                                             Thraustochytrium U42-2                                                                         20891     8/8/88                                             Schizochytrium 23B                                                                             20892     8/8/88                                             ______________________________________                                    

The present invention, while disclosed in terms of specific organismstrains, is intended to include all such methods and strains obtainableand useful according to the teachings disclosed herein, including allsuch substitutions, modifications, and optimizations as would beavailable expedients to those of ordinary skill in the art.

REFERENCES

Ainsworth, G. C. (1973) "Introduction and keys to the higher taxa." In:The Fungi. An Advanced Treatise. Vol. 4B, G. C. Ainsworth et al. (eds.),Academic Press, New York, pp. 107.

Bahnweg, G. & Jackle, I (1986) "A new approach to taxonomy of theThraustochytriales and Lybrinthulales." In: The Biology of Marine Fungi,S. T. Moss (ed.), Cambridge University Press, London, pp. 131-140.

Barr, J. S. (1981) "The phylogenetic and taxonomic implications offlagellar rootlet morphology among zoosporic fungi." BioSystems14:359-370.

Barr, J. S. (1983) "The zoosporic grouping of plant pathogens." In:Zoosporic Plant Pathogens: a modern perspective, S. T. Buczacki (ed.),Academic Press, pp. 43-83.

Bartnicki-Garcia, S. (1988) "The cell wall: a crucial structure infungal evolution." In: Evolutionary Biology of the Fungi, A. D. M.Rayner et al. (eds.), Cambridge University Press, pp. 389-403.

CalBiochem Co. (1987). Biochemical/Immunochemical Catalog. BehringDiagnostics, La Jolla, Calif.

Cavalier-Smith, T. (1975) "The origin of nuclei and of eukaryoticcells." Nature 256:463-468.

Cavalier-Smith, T. (1983) "A 6-kingdom classification and a unifiedphylogeny." In: Endocytobiology II: Intracellular Space as OligogeneticSystem, H. E. A. Schenk and W. Schwemmler (eds.), De Gruyter (Berlin),pp. 1027-1034.

Chamberlain, A. H. and Moss, S. T. (1988) "The thraustochytrids: aprotist group with mixed affinities." BioSystems 21:341-349.

Cerda-Olmeda, E. & Lipson, E. (1987) Phycomyes, Cold Springs HarborLaboratory, Cold Springs Harbor, N.Y.

Dick, M. W. (1973) "Saprolegniales." In: The Fungi. An AdvancedTreatise, Vo. 4B, G. C. Ainsworth et al. (eds.), Academic Press, NewYork, pp. 113-144.

Ellenbogen, B. B. et al. (1969) "Polyunsaturated fatty acids of aquaticfungi: possible phylogenetic significance." Comp. Biochem. Physiol.29:805-811.

Emerson, R. (1950) "Current trends of experimental research in theaquatic Physomycetes." Ann. Rev. Micro. 4:169-200.

Erwin, J. (1973). "Comparative biochemistry of fatty acids in eukaryoticmicroorganisms." In: Lipids and Biomembranes of EukaryoticMicroorganisms, J. Erwin (ed.), Academic Press, New York, pp. 41-143.

Findlay, R. H. et al. (1986) "Biochemical indicators of the role offungi and Thraustrochytrids in mangrove detrital systems." In: TheBiology of Marine Fungi, S. T. Moss (ed.), Cambridge University Press,London, pp. 91-103.

Fuller, M. S. et al. (1964) "Isolation and pure culture of marinePhycomycetes." Mycologia 56:745-756.

Gellerman, J. L. & Schlenk, H. (1979) "Methyl-directed desaturation ofarachidonic to eicosapentaenoic acid int eh fungus, Saprolengnia parasitica." Biochem. Biophys. Acta 573:23-30.

Goldstein, S. (1963) "Development and nutrition of new species ofThraustochytrium." Am. J. Bot. 50:271-279.

Goldstein, S. et al. (1969) "Biology of a problematic marine fungus,Dermocystidium sp. II. Nutrition and repiration." Mycologia 61:468-72.

Hori, H. et al. (1980) Nucl. Acids Res. 8:5535-5539.

Hunter, J. E. (1987) "Fish oil and other omega-3 sources." J. Am. OilChem. Soc. 64:1592-1596.

Kates, M. (1986) Techniques of LIpidology: Isolation, Analysis andIdentification of Lipids, Elsevier, Amsterdam.

Kazama, F (1980) "The zoospore of Schizoshytrium aggregatum. Can J. Bot.58:2434-2446.

Kyle, D. J. (1987) "Microalgae as a source of EPA-containing oils."Abstract of talk presented at World Conference for Fats & Oils, Hamburg,West Germany. J. Am. Oil Chem. Soc. 64:1251.

Leedale, G. (1974) "How many are the kingdoms of organisms." Taxon23:261-270.

Lepage, G. and Roy, C. (1984) "Improved recovery of fatty acid throughdirect transesterification without prior extraction or purification." J.Lipid Res. 25:1391-1396.

Margulis, L. (1970) Origin of Eukaryotic Cell, Yale University Press,New Haven.

Margulis, L. and Sagan, D. (1985) "Order amidst animalcules: theProctoctista kingdom and its undulipodiated cells." BioSystems18:141-147.

Mannella, C. A. et al. (1987) "Interrelatedness of 5S RNA sequencesinvestigated by correspondence analysis." J. Mol. Evol. 24:228-235.

Moss, S. (1986) "Biology and phylogeny of the Labrinthulales andThraustochytriales." In: The Biology of Marine Fungi, S. T. Moss (ed.),Cambridge University Press, London, pp. 105-130.

Perkins, F. O. (1976) "Fine structure of lower marine and estuarinefungi." In: Recent Advances in marine Mycology, E. B. Gareth Jones(ed.), Elek Science, pp. 279-312.

Pigot, G. M. (1989), "The need to improve omega-3 content of culturedfish," World Aquaculture 20:63-68)

Perkins, F. (1974) "Phylogenetic considerations of the problematicthraustochytriaceous-labrinthulid-Dermocystidium complex based onobservations of fine structure." Veroff. Inst. Meeresforsch. Bremerh.Suppl. 5:45-63.

Pohl, P. and Zurheide, F. (1979) "Fatty acids and lipids of marine algaeand the control of their biosynthesis by environmental factors." In:Marine Algae in Pharmaceutical Science, H. Hoppe et al. (eds.), W. deGruyter, Berlin, pp. 473-524.

Poyton, R. (1970) "The characteristization of Hyallochlorella marinagen. et sp. nov. a new colorless counterpart of Chlorella." J. Gen.Microbiol. 62:171-188.

Pyther, J. H. (1983) "Cultivation of Macroscopic marine algae." In:Solar Energy Research Institute Aquatic Species Program Review. Proc ofthe March 1983 Principal Investigators Meeting. SERI/CP-231-1946, pp.7914 88.

Sargent, J. eg al. (1989), "The lipids," in Fish Nutrition, SecondEdition, J. Halver (ed.), Academic Press, pp. 153-218.

Schlenk, H. (1954) "Urea inclusion compounds of fatty acids." Prog.Chem. Fats and Other Lipids 2:243:267.

Schneider, J. (1976) "Cultivation of Microorganisms. Section 3.2: Fung."In: Marine Ecology, Vol. 3, Part 1. Cultivation, O. Kinne (ed.), WileyInterscience.

Sigma Chemical Co. (1988). Catalog: Biochemical and Organic Compoundsfor Research. Sigma Chemical Co., St. Louis, Mo.

Simopoulos, A. P. et al. (1986) Health Effects of Polyunsaturated FattyAcids in Seafoods, Academic Press, New York.

Sorokin, C. (1973) "Growth measurements: dry weight packed cell volume,and optical density." In: Handbook of Phycological Methods: CultureMethods and Growth Measurements, J. R. Stein (ed.), Cambridge Universitypress, Cambridge, pp. 321-343.

Sparrow, F. K. (1960) Aquatic Phycomycetes. University of MichiganPress, Ann Arbor, pp.. 37-38.

Wassef, M. (1977) "Fungal lipids." Adv. Lipid Res. 15:159-232.

Wette, J. D. (1980) Lipid Biochemistry of Fungi and Other Organisms.Plenum Press, New York.

Yamada, H. et al. (1987) "Production of arachidonic acid andeicosapentaenoic acid by microorganisms." Abstract of talk presented atWold Conference for Fats & Oils, Hamburg, West Germany. J. Am Oil Chem.Soc. 64:1254.

What is claimed is:
 1. A food product, comprising:a) microorganismsselected from the group consisting of microorganisms of the genusThraustochytrium, microorganisms of the genus Schizochytrium andmixtures thereof, wherein said microorganisms are capable of effectivelyproducing omega-3 highly unsaturated fatty acid under conditionscomprising: i) salinity levels less than salinity levels found inseawater; andii) a temperature of at least about 15° C.; and b) foodmaterial.
 2. A food product, as claimed in claim 1, wherein said foodmaterial is animal food.
 3. A food product, as claimed in claim 1,wherein said food material is human food.
 4. A food product, as claimedin claim 1, further comprising an antioxidant added to a fermentationmedium prior to harvesting of said microorganisms or added to said foodproduct during post-harvest processing of said microorganisms.
 5. A foodproduct, as claimed in claim 1, wherein said food product is packagedunder non-oxidizing conditions.
 6. A food product, as claimed in claim1, wherein said food product is extruded to manipulate by degree of cellrupture the bioavailability of omega-3 highly unsaturated fatty acidscontained in said microorganisms.
 7. A food product, as claimed in claim1, wherein said food product is extruded to reduce the amount of oxygenthat reaches the omega-3 highly unsaturated fatty acid as compared tothe amount of oxygen that would reach the omega-3 highly unsaturatedfatty acid in an analogous food product which has not been extruded. 8.A food product, as claimed in claim 1, wherein said microorganisms havebeen cultured in a medium comprising a sodium concentration less thanabout 6.58 g/l.
 9. A food product, as claimed in claim 1, wherein saidmicroorganisms have been cultured in a medium comprising a sodiumconcentration less than about 4.61 g/l.
 10. A food product, as claimedin claim 1, wherein said microorganisms are selected from the groupconsisting of:(i) Schizochytrium having the identifying characteristicsof ATCC Accession No. 20888 and mutant strains derived therefrom,wherein, said mutant strains derived therefrom are capable of producingomega-3 highly unsaturated fatty acid; (ii) Schizochytrium having theidentifying characteristics of ATCC Accession No. 20889 and mutantstrains derived therefrom, wherein, said mutant strains derivedtherefrom are capable of producing omega-3 highly unsaturated fattyacid; (iii) Thraustochytrium having the identifying characteristics ofATCC Accession No. 20890 and mutant strains derived therefrom, wherein,said mutant strains derived therefrom are capable or producing omega-3highly unsaturated fatty acid; (iv) Thraustochytrium having theidentifying characteristics of ATCC Accession No. 20891 and mutantstrains derived therefrom, wherein, said mutant strains derivedtherefrom are capable of producing omega-3 highly unsaturated fattyacid; and (v) Thraustochytrium having the identifying characteristics ofATCC Accession No. 20892 and mutant strains derived therefrom, wherein,said mutant strains derived therefrom are capable of producing omega-3highly unsaturated fatty acid.